diff --git a/14-arrays/13-project-clock/01-printing-the-digits/README.md b/15-project-retro-led-clock/01-printing-the-digits/README.md
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diff --git a/14-arrays/13-project-clock/02-printing-the-clock/main.go b/15-project-retro-led-clock/02-printing-the-clock/main.go
similarity index 100%
rename from 14-arrays/13-project-clock/02-printing-the-clock/main.go
rename to 15-project-retro-led-clock/02-printing-the-clock/main.go
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diff --git a/14-arrays/13-project-clock/03-animating-the-clock/README.md b/15-project-retro-led-clock/03-animating-the-clock/README.md
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rename from 14-arrays/13-project-clock/03-animating-the-clock/README.md
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diff --git a/14-arrays/13-project-clock/04-blinking-the-separators/README.md b/15-project-retro-led-clock/04-blinking-the-separators/README.md
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rename from 14-arrays/13-project-clock/04-blinking-the-separators/main.go
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diff --git a/14-arrays/13-project-clock/04-blinking-the-separators/solution/main.go b/15-project-retro-led-clock/04-blinking-the-separators/solution/main.go
similarity index 100%
rename from 14-arrays/13-project-clock/04-blinking-the-separators/solution/main.go
rename to 15-project-retro-led-clock/04-blinking-the-separators/solution/main.go
diff --git a/14-arrays/13-project-clock/05-full-annotated-solution/main.go b/15-project-retro-led-clock/05-full-annotated-solution/main.go
similarity index 100%
rename from 14-arrays/13-project-clock/05-full-annotated-solution/main.go
rename to 15-project-retro-led-clock/05-full-annotated-solution/main.go
diff --git a/14-arrays/13-project-clock/README.md b/15-project-retro-led-clock/README.md
similarity index 76%
rename from 14-arrays/13-project-clock/README.md
rename to 15-project-retro-led-clock/README.md
index 088ec60..9353567 100644
--- a/14-arrays/13-project-clock/README.md
+++ b/15-project-retro-led-clock/README.md
@@ -11,26 +11,26 @@
 
 ## GOALS:
 
-### 👉 [STEP #1 — Print the Digits](https://github.com/inancgumus/learngo/tree/master/14-arrays/13-project-clock/01-printing-the-digits/)
+### 👉 [STEP #1 — Print the Digits](https://github.com/inancgumus/learngo/tree/master/15-project-retro-clock/01-printing-the-digits/)
 - [ ] Define a new placeholder type
 - [ ] Create the digit arrays from 0 to 9
 - [ ] Put them into the "digits" array
 - [ ] Print them side-by-side
 
-### 👉 [STEP #2 — Print the Clock](https://github.com/inancgumus/learngo/tree/master/14-arrays/13-project-clock/02-printing-the-clock/)
+### 👉 [STEP #2 — Print the Clock](https://github.com/inancgumus/learngo/tree/master/15-project-retro-clock/02-printing-the-clock/)
 - [ ] Get the current time
 - [ ] Create the clock array
 - [ ] Print the clock
 - [ ] Add the separators
 
-### 👉 [STEP #3 — Animate the Clock](https://github.com/inancgumus/learngo/tree/master/14-arrays/13-project-clock/03-animating-the-clock/)
+### 👉 [STEP #3 — Animate the Clock](https://github.com/inancgumus/learngo/tree/master/15-project-retro-clock/03-animating-the-clock/)
 - [ ] Create an infinite loop to update the clock
 - [ ] Update the clock every second
 - [ ] Clear the screen before the infinite loop
 - [ ] Move the cursor to the top-left corner of the screen before each
       step of the infinite loop
 
-### 👉 [BONUS: STEP #4 — Blink the Clock](https://github.com/inancgumus/learngo/tree/master/14-arrays/13-project-clock/04-blinking-the-separators/)
+### 👉 [BONUS: STEP #4 — Blink the Clock](https://github.com/inancgumus/learngo/tree/master/15-project-retro-clock/04-blinking-the-separators/)
 - [ ] Blink the separators
 
-### 👉 [FULL ANNOTATED SOLUTION](https://github.com/inancgumus/learngo/tree/master/14-arrays/13-project-clock/05-full-annotated-solution/main.go)
\ No newline at end of file
+### 👉 [FULL ANNOTATED SOLUTION](https://github.com/inancgumus/learngo/tree/master/15-project-retro-clock/05-full-annotated-solution/main.go)
\ No newline at end of file
diff --git a/14-arrays/13-project-clock/exercises/01-refactor/main.go b/15-project-retro-led-clock/exercises/01-refactor/main.go
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similarity index 100%
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diff --git a/14-arrays/13-project-clock/exercises/01-refactor/solution/placeholders.go b/15-project-retro-led-clock/exercises/01-refactor/solution/placeholders.go
similarity index 100%
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similarity index 100%
rename from 14-arrays/13-project-clock/exercises/02-alarm/placeholders.go
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similarity index 100%
rename from 14-arrays/13-project-clock/exercises/02-alarm/solution/main.go
rename to 15-project-retro-led-clock/exercises/02-alarm/solution/main.go
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similarity index 100%
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rename to 15-project-retro-led-clock/exercises/03-split-second/placeholders.go
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similarity index 100%
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similarity index 100%
rename from 14-arrays/13-project-clock/exercises/04-ticker/solution/main.go
rename to 15-project-retro-led-clock/exercises/04-ticker/solution/main.go
diff --git a/14-arrays/13-project-clock/exercises/04-ticker/solution/placeholders.go b/15-project-retro-led-clock/exercises/04-ticker/solution/placeholders.go
similarity index 100%
rename from 14-arrays/13-project-clock/exercises/04-ticker/solution/placeholders.go
rename to 15-project-retro-led-clock/exercises/04-ticker/solution/placeholders.go
diff --git a/14-arrays/13-project-clock/exercises/README.md b/15-project-retro-led-clock/exercises/README.md
similarity index 80%
rename from 14-arrays/13-project-clock/exercises/README.md
rename to 15-project-retro-led-clock/exercises/README.md
index c206544..65aebd4 100644
--- a/14-arrays/13-project-clock/exercises/README.md
+++ b/15-project-retro-led-clock/exercises/README.md
@@ -2,20 +2,20 @@
 
 These exercises will reinforce your knowledge of manipulating arrays. You will prove yourself that you can write easy to maintain Go programs.
 
-1. **[Refactor](https://github.com/inancgumus/learngo/tree/master/14-arrays/13-project-clock/exercises/01-refactor)**
+1. **[Refactor](https://github.com/inancgumus/learngo/tree/master/15-project-retro-led-clock/exercises/01-refactor)**
 
   In this exercise, you will refactor the project to multiple files by moving
   all the placeholders. This will make the project easy to maintain down the road.
 
-2. **[Set an Alarm](https://github.com/inancgumus/learngo/tree/master/14-arrays/13-project-clock/exercises/02-alarm)**
+2. **[Set an Alarm](https://github.com/inancgumus/learngo/tree/master/15-project-retro-led-clock/exercises/02-alarm)**
 
   You will print " ALARM! " every 10 seconds.
 
-3. **[Split Second](https://github.com/inancgumus/learngo/tree/master/14-arrays/13-project-clock/exercises/03-split-second)**
+3. **[Split Second](https://github.com/inancgumus/learngo/tree/master/15-project-retro-led-clock/exercises/03-split-second)**
 
   You will display the split second in the clock, you will need to update the
   clock every 1/10th of a second instead of every second.
 
-4. **[Ticker](https://github.com/inancgumus/learngo/tree/master/14-arrays/13-project-clock/exercises/04-ticker)**
+4. **[Ticker](https://github.com/inancgumus/learngo/tree/master/15-project-retro-led-clock/exercises/04-ticker)**
 
   This is an HARD EXERCISE. You will slide the clock animation from right-to-left. After this exercise, you will truly feel that you've mastered everything you've learned so far.
\ No newline at end of file
diff --git a/15-slices/exercises/README.md b/15-slices/exercises/README.md
deleted file mode 100644
index 2d40194..0000000
--- a/15-slices/exercises/README.md
+++ /dev/null
@@ -1,31 +0,0 @@
-# Slice Exercises
-
-## Exercises Level I - Basics — Warm-Up
-
-1. **[Declare nil slices](https://github.com/inancgumus/learngo/tree/master/15-slices/exercises/01-declare-nil)**
-
-2. **[Assign empty slices](https://github.com/inancgumus/learngo/tree/master/15-slices/exercises/02-empty)**
-
-3. **[Assign slice literals](https://github.com/inancgumus/learngo/tree/master/15-slices/exercises/03-slice-literal)**
-
-4. **[Declare the arrays as slices](https://github.com/inancgumus/learngo/tree/master/15-slices/exercises/04-declare-arrays-as-slices)**
-
-5. **[Fix the Problems](https://github.com/inancgumus/learngo/tree/master/15-slices/exercises/05-fix-the-problems)**
-
-6. **[Compare the slices](https://github.com/inancgumus/learngo/tree/master/15-slices/exercises/06-compare-the-slices)**
-
----
-
-## Exercises Level II - Appending
-
-1. **[Append #1 — Append and compare byte slices](https://github.com/inancgumus/learngo/tree/master/15-slices/exercises/07-append)**
-
-2. **[Append #2 — Append to a nil slice](https://github.com/inancgumus/learngo/tree/master/15-slices/exercises/08-append-2)**
-
-3. **[Append #3 — Fix the problems](https://github.com/inancgumus/learngo/tree/master/15-slices/exercises/09-append-3-fix)**
-
-4. **[Append #4 — Sort and write items to a file](https://github.com/inancgumus/learngo/tree/master/15-slices/exercises/10-append-4-sort-to-a-file)**
-
-5. **[Append #5 — Sort and write items to a file with their ordinals](https://github.com/inancgumus/learngo/tree/master/15-slices/exercises/11-append-5-sort-to-a-file)**
-
-5. **[Append #6 — Find and write the names of subdirectories to a file](https://github.com/inancgumus/learngo/tree/master/15-slices/exercises/12-append-6-print-directories)**
\ No newline at end of file
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diff --git a/15-slices/exercises/05-fix-the-problems/solution/main.go b/16-slices/exercises/05-fix-the-problems/solution/main.go
similarity index 100%
rename from 15-slices/exercises/05-fix-the-problems/solution/main.go
rename to 16-slices/exercises/05-fix-the-problems/solution/main.go
diff --git a/15-slices/exercises/06-compare-the-slices/main.go b/16-slices/exercises/06-compare-the-slices/main.go
similarity index 100%
rename from 15-slices/exercises/06-compare-the-slices/main.go
rename to 16-slices/exercises/06-compare-the-slices/main.go
diff --git a/15-slices/exercises/06-compare-the-slices/solution/main.go b/16-slices/exercises/06-compare-the-slices/solution/main.go
similarity index 100%
rename from 15-slices/exercises/06-compare-the-slices/solution/main.go
rename to 16-slices/exercises/06-compare-the-slices/solution/main.go
diff --git a/15-slices/exercises/07-append/main.go b/16-slices/exercises/07-append/main.go
similarity index 100%
rename from 15-slices/exercises/07-append/main.go
rename to 16-slices/exercises/07-append/main.go
diff --git a/15-slices/exercises/07-append/solution/main.go b/16-slices/exercises/07-append/solution/main.go
similarity index 100%
rename from 15-slices/exercises/07-append/solution/main.go
rename to 16-slices/exercises/07-append/solution/main.go
diff --git a/15-slices/exercises/08-append-2/main.go b/16-slices/exercises/08-append-2/main.go
similarity index 100%
rename from 15-slices/exercises/08-append-2/main.go
rename to 16-slices/exercises/08-append-2/main.go
diff --git a/15-slices/exercises/08-append-2/solution/main.go b/16-slices/exercises/08-append-2/solution/main.go
similarity index 100%
rename from 15-slices/exercises/08-append-2/solution/main.go
rename to 16-slices/exercises/08-append-2/solution/main.go
diff --git a/15-slices/exercises/09-append-3-fix/main.go b/16-slices/exercises/09-append-3-fix/main.go
similarity index 100%
rename from 15-slices/exercises/09-append-3-fix/main.go
rename to 16-slices/exercises/09-append-3-fix/main.go
diff --git a/15-slices/exercises/09-append-3-fix/solution/main.go b/16-slices/exercises/09-append-3-fix/solution/main.go
similarity index 100%
rename from 15-slices/exercises/09-append-3-fix/solution/main.go
rename to 16-slices/exercises/09-append-3-fix/solution/main.go
diff --git a/16-slices/exercises/README.md b/16-slices/exercises/README.md
new file mode 100644
index 0000000..d03b9d5
--- /dev/null
+++ b/16-slices/exercises/README.md
@@ -0,0 +1,25 @@
+# Slice Exercises
+
+## Exercises Level I - Basics — Warm-Up
+
+1. **[Declare nil slices](https://github.com/inancgumus/learngo/tree/master/16-slices/exercises/01-declare-nil)**
+
+2. **[Assign empty slices](https://github.com/inancgumus/learngo/tree/master/16-slices/exercises/02-empty)**
+
+3. **[Assign slice literals](https://github.com/inancgumus/learngo/tree/master/16-slices/exercises/03-slice-literal)**
+
+4. **[Declare the arrays as slices](https://github.com/inancgumus/learngo/tree/master/16-slices/exercises/04-declare-arrays-as-slices)**
+
+5. **[Fix the Problems](https://github.com/inancgumus/learngo/tree/master/16-slices/exercises/05-fix-the-problems)**
+
+6. **[Compare the slices](https://github.com/inancgumus/learngo/tree/master/16-slices/exercises/06-compare-the-slices)**
+
+---
+
+## Exercises Level II - Appending
+
+1. **[Append #1 — Append and compare byte slices](https://github.com/inancgumus/learngo/tree/master/16-slices/exercises/07-append)**
+
+2. **[Append #2 — Append to a nil slice](https://github.com/inancgumus/learngo/tree/master/16-slices/exercises/08-append-2)**
+
+3. **[Append #3 — Fix the problems](https://github.com/inancgumus/learngo/tree/master/16-slices/exercises/09-append-3-fix)**
\ No newline at end of file
diff --git a/15-slices/questions/1-slices-vs-arrays.md b/16-slices/questions/1-slices-vs-arrays.md
similarity index 100%
rename from 15-slices/questions/1-slices-vs-arrays.md
rename to 16-slices/questions/1-slices-vs-arrays.md
diff --git a/15-slices/questions/2-appending.md b/16-slices/questions/2-appending.md
similarity index 100%
rename from 15-slices/questions/2-appending.md
rename to 16-slices/questions/2-appending.md
diff --git a/15-slices/questions/README.md b/16-slices/questions/README.md
similarity index 100%
rename from 15-slices/questions/README.md
rename to 16-slices/questions/README.md
diff --git a/x-tba/slices/07-slice-expressions/1-theory/main.go b/x-tba/slices/07-slice-expressions/1-theory/main.go
deleted file mode 100644
index 6951b2b..0000000
--- a/x-tba/slices/07-slice-expressions/1-theory/main.go
+++ /dev/null
@@ -1,38 +0,0 @@
-// For more tutorials: https://blog.learngoprogramming.com
-//
-// Copyright © 2018 Inanc Gumus
-// Learn Go Programming Course
-// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
-//
-
-package main
-
-import (
-	s "github.com/inancgumus/prettyslice"
-)
-
-func main() {
-	msg := []byte{'h', 'e', 'l', 'l', 'o'}
-	s.Show("msg", msg)
-
-	s.Show("msg[0:1]", msg[0:1])
-	s.Show("msg[0:2]", msg[0:2])
-	s.Show("msg[0:3]", msg[0:3])
-	s.Show("msg[0:4]", msg[0:4])
-	s.Show("msg[0:5]", msg[0:5])
-
-	// default indexes
-	s.Show("msg[0:]", msg[0:])
-	s.Show("msg[:5]", msg[:5])
-	s.Show("msg[:]", msg[:])
-
-	// error: beyond
-	// s.Show("msg", msg)[:6]
-
-	s.Show("msg[1:4]", msg[1:4])
-
-	s.Show("msg[1:5]", msg[1:5])
-	s.Show("msg[1:]", msg[1:])
-
-	s.Show("append(msg)", append(msg[:4], '!'))
-}
diff --git a/x-tba/slices/07-slice-expressions/2-example/main.go b/x-tba/slices/07-slice-expressions/2-example/main.go
deleted file mode 100644
index b30172b..0000000
--- a/x-tba/slices/07-slice-expressions/2-example/main.go
+++ /dev/null
@@ -1,59 +0,0 @@
-// For more tutorials: https://blog.learngoprogramming.com
-//
-// Copyright © 2018 Inanc Gumus
-// Learn Go Programming Course
-// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
-//
-
-package main
-
-import (
-	"fmt"
-
-	s "github.com/inancgumus/prettyslice"
-)
-
-func main() {
-	// think of this as search results of a search engine.
-	// it could have been fetched from a database
-	items := []string{
-		"pacman",
-		"mario",
-		"tetris",
-		"doom",
-		"galaga",
-		"frogger",
-		"asteroids",
-		"simcity",
-		"metroid",
-		"defender",
-		"rayman",
-		"tempest",
-		"ultima",
-	}
-
-	s.MaxPerLine = 4
-	s.Show("All items", items)
-
-	top3 := items[:3]
-	s.Show("Top 3 items", top3)
-
-	l := len(items)
-
-	// you can use variables in a slice expression
-	last4 := items[l-4:]
-	s.Show("Last 4 items", last4)
-
-	// reslicing: slicing another sliced slice
-	mid := last4[1:3]
-	s.Show("Last4[1:3]", mid)
-
-	// the same elements can be in different indexes
-	// fmt.Println(items[9], last4[0])
-
-	// slicing returns a slice with the same type of the sliced slice
-	fmt.Printf("slicing : %T %[1]q\n", items[2:3])
-
-	// indexing returns a single element with the type of the indexed slice's element type
-	fmt.Printf("indexing: %T %[1]q\n", items[2])
-}
diff --git a/x-tba/slices/08-slice-expressions-pagination/main.go b/x-tba/slices/08-slice-expressions-pagination/main.go
deleted file mode 100644
index 531407b..0000000
--- a/x-tba/slices/08-slice-expressions-pagination/main.go
+++ /dev/null
@@ -1,58 +0,0 @@
-// For more tutorials: https://blog.learngoprogramming.com
-//
-// Copyright © 2018 Inanc Gumus
-// Learn Go Programming Course
-// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
-//
-
-package main
-
-import (
-	"fmt"
-
-	s "github.com/inancgumus/prettyslice"
-)
-
-func main() {
-	// think of this as search results of a search engine.
-	// it could have been fetched from a database
-	items := []string{
-		"pacman",
-		"mario",
-		"tetris",
-		"doom",
-		"galaga",
-		"frogger",
-		"asteroids",
-		"simcity",
-		"metroid",
-		"defender",
-		"rayman",
-		"tempest",
-		"ultima",
-	}
-
-	// s.Show("0:4", items[0:4])
-	// s.Show("4:8", items[4:8])
-	// s.Show("8:12", items[8:12])
-	// s.Show("12:13", items[12:13])
-	// s.Show("12:14", items[12:14]) // error
-
-	l := len(items)
-
-	const pageSize = 4
-
-	for from := 0; from < l; from += pageSize {
-		to := from + pageSize
-		if to > l {
-			to = l
-		}
-
-		// fmt.Printf("%d:%d\n", from, to)
-
-		currentPage := items[from:to]
-
-		head := fmt.Sprintf("Page #%d", (from/pageSize)+1)
-		s.Show(head, currentPage)
-	}
-}
diff --git a/x-tba/slices/13-png-parser/2-png-anatomy-example.md b/x-tba/slices/13-png-parser/2-png-anatomy-example.md
deleted file mode 100644
index 7d4df1a..0000000
--- a/x-tba/slices/13-png-parser/2-png-anatomy-example.md
+++ /dev/null
@@ -1,26 +0,0 @@
-# The Brief Anatomy of a PNG image
-
-```
-The first 24 bytes:
-
-PNG HEADER:
-╔═════╗╔════╗╔════╗╔════╗╔════╗╔════╗╔════╗╔════╗
-║ 137 ║║ 80 ║║ 78 ║║ 71 ║║ 13 ║║ 10 ║║ 26 ║║ 10 ║
-╚═════╝╚════╝╚════╝╚════╝╚════╝╚════╝╚════╝╚════╝
-   0      1     2     3     4     5     6     7
-
-CHUNK LENGTH         CHUNK TYPE (IHDR)
-╔═══╗╔═══╗╔═══╗╔════╗╔════╗╔════╗╔════╗╔════╗
-║ 0 ║║ 0 ║║ 0 ║║ 13 ║║ 73 ║║ 72 ║║ 68 ║║ 82 ║
-╚═══╝╚═══╝╚═══╝╚════╝╚════╝╚════╝╚════╝╚════╝
-  8    9   10    11    12    13    14    15
-
-(      Unsigned 32-bit integers          )
-WIDTH                HEIGHT
-╔═══╗╔═══╗╔═══╗╔════╗╔═══╗╔═══╗╔═══╗╔════╗
-║ 0 ║║ 0 ║║ 2 ║║ 76 ║║ 0 ║║ 0 ║║ 3 ║║ 32 ║
-╚═══╝╚═══╝╚═══╝╚════╝╚═══╝╚═══╝╚═══╝╚════╝
- 16   17   18    19   20   21   22    23
-
-... Other bytes in the png image ...
-```
\ No newline at end of file
diff --git a/15-slices/06-empty-file-finder-project-reading-empty-files/files/empty1.txt b/x-tba/slices/19-empty-file-finder-project/1st-version-reading-empty-files/files/empty1.txt
similarity index 100%
rename from 15-slices/06-empty-file-finder-project-reading-empty-files/files/empty1.txt
rename to x-tba/slices/19-empty-file-finder-project/1st-version-reading-empty-files/files/empty1.txt
diff --git a/15-slices/06-empty-file-finder-project-reading-empty-files/files/empty2.txt b/x-tba/slices/19-empty-file-finder-project/1st-version-reading-empty-files/files/empty2.txt
similarity index 100%
rename from 15-slices/06-empty-file-finder-project-reading-empty-files/files/empty2.txt
rename to x-tba/slices/19-empty-file-finder-project/1st-version-reading-empty-files/files/empty2.txt
diff --git a/15-slices/06-empty-file-finder-project-reading-empty-files/files/empty3.txt b/x-tba/slices/19-empty-file-finder-project/1st-version-reading-empty-files/files/empty3.txt
similarity index 100%
rename from 15-slices/06-empty-file-finder-project-reading-empty-files/files/empty3.txt
rename to x-tba/slices/19-empty-file-finder-project/1st-version-reading-empty-files/files/empty3.txt
diff --git a/15-slices/06-empty-file-finder-project-reading-empty-files/files/nonEmpty1.txt b/x-tba/slices/19-empty-file-finder-project/1st-version-reading-empty-files/files/nonEmpty1.txt
similarity index 100%
rename from 15-slices/06-empty-file-finder-project-reading-empty-files/files/nonEmpty1.txt
rename to x-tba/slices/19-empty-file-finder-project/1st-version-reading-empty-files/files/nonEmpty1.txt
diff --git a/15-slices/06-empty-file-finder-project-reading-empty-files/files/nonEmpty2.txt b/x-tba/slices/19-empty-file-finder-project/1st-version-reading-empty-files/files/nonEmpty2.txt
similarity index 100%
rename from 15-slices/06-empty-file-finder-project-reading-empty-files/files/nonEmpty2.txt
rename to x-tba/slices/19-empty-file-finder-project/1st-version-reading-empty-files/files/nonEmpty2.txt
diff --git a/15-slices/06-empty-file-finder-project-reading-empty-files/files/nonEmpty3.txt b/x-tba/slices/19-empty-file-finder-project/1st-version-reading-empty-files/files/nonEmpty3.txt
similarity index 100%
rename from 15-slices/06-empty-file-finder-project-reading-empty-files/files/nonEmpty3.txt
rename to x-tba/slices/19-empty-file-finder-project/1st-version-reading-empty-files/files/nonEmpty3.txt
diff --git a/15-slices/06-empty-file-finder-project-reading-empty-files/main.go b/x-tba/slices/19-empty-file-finder-project/1st-version-reading-empty-files/main.go
similarity index 100%
rename from 15-slices/06-empty-file-finder-project-reading-empty-files/main.go
rename to x-tba/slices/19-empty-file-finder-project/1st-version-reading-empty-files/main.go
diff --git a/15-slices/07-empty-file-finder-project-writing-to-a-file/files/empty1.txt b/x-tba/slices/19-empty-file-finder-project/2nd-version-writing-to-a-file/files/empty1.txt
similarity index 100%
rename from 15-slices/07-empty-file-finder-project-writing-to-a-file/files/empty1.txt
rename to x-tba/slices/19-empty-file-finder-project/2nd-version-writing-to-a-file/files/empty1.txt
diff --git a/15-slices/07-empty-file-finder-project-writing-to-a-file/files/empty2.txt b/x-tba/slices/19-empty-file-finder-project/2nd-version-writing-to-a-file/files/empty2.txt
similarity index 100%
rename from 15-slices/07-empty-file-finder-project-writing-to-a-file/files/empty2.txt
rename to x-tba/slices/19-empty-file-finder-project/2nd-version-writing-to-a-file/files/empty2.txt
diff --git a/15-slices/07-empty-file-finder-project-writing-to-a-file/files/empty3.txt b/x-tba/slices/19-empty-file-finder-project/2nd-version-writing-to-a-file/files/empty3.txt
similarity index 100%
rename from 15-slices/07-empty-file-finder-project-writing-to-a-file/files/empty3.txt
rename to x-tba/slices/19-empty-file-finder-project/2nd-version-writing-to-a-file/files/empty3.txt
diff --git a/15-slices/07-empty-file-finder-project-writing-to-a-file/files/nonEmpty1.txt b/x-tba/slices/19-empty-file-finder-project/2nd-version-writing-to-a-file/files/nonEmpty1.txt
similarity index 100%
rename from 15-slices/07-empty-file-finder-project-writing-to-a-file/files/nonEmpty1.txt
rename to x-tba/slices/19-empty-file-finder-project/2nd-version-writing-to-a-file/files/nonEmpty1.txt
diff --git a/15-slices/07-empty-file-finder-project-writing-to-a-file/files/nonEmpty2.txt b/x-tba/slices/19-empty-file-finder-project/2nd-version-writing-to-a-file/files/nonEmpty2.txt
similarity index 100%
rename from 15-slices/07-empty-file-finder-project-writing-to-a-file/files/nonEmpty2.txt
rename to x-tba/slices/19-empty-file-finder-project/2nd-version-writing-to-a-file/files/nonEmpty2.txt
diff --git a/15-slices/07-empty-file-finder-project-writing-to-a-file/files/nonEmpty3.txt b/x-tba/slices/19-empty-file-finder-project/2nd-version-writing-to-a-file/files/nonEmpty3.txt
similarity index 100%
rename from 15-slices/07-empty-file-finder-project-writing-to-a-file/files/nonEmpty3.txt
rename to x-tba/slices/19-empty-file-finder-project/2nd-version-writing-to-a-file/files/nonEmpty3.txt
diff --git a/15-slices/07-empty-file-finder-project-writing-to-a-file/main.go b/x-tba/slices/19-empty-file-finder-project/2nd-version-writing-to-a-file/main.go
similarity index 100%
rename from 15-slices/07-empty-file-finder-project-writing-to-a-file/main.go
rename to x-tba/slices/19-empty-file-finder-project/2nd-version-writing-to-a-file/main.go
diff --git a/15-slices/exercises/10-append-4-sort-to-a-file/main.go b/x-tba/slices/19-empty-file-finder-project/exercises/1-sort-to-a-file/main.go
similarity index 95%
rename from 15-slices/exercises/10-append-4-sort-to-a-file/main.go
rename to x-tba/slices/19-empty-file-finder-project/exercises/1-sort-to-a-file/main.go
index f2079a6..71eb476 100644
--- a/15-slices/exercises/10-append-4-sort-to-a-file/main.go
+++ b/x-tba/slices/19-empty-file-finder-project/exercises/1-sort-to-a-file/main.go
@@ -1,7 +1,7 @@
 package main
 
 // ---------------------------------------------------------
-// EXERCISE: Append #4 — Sort to a file
+// EXERCISE: Sort to a file
 //
 //  1. Get arguments from command-line
 //
diff --git a/15-slices/exercises/10-append-4-sort-to-a-file/solution/main.go b/x-tba/slices/19-empty-file-finder-project/exercises/1-sort-to-a-file/solution/main.go
similarity index 100%
rename from 15-slices/exercises/10-append-4-sort-to-a-file/solution/main.go
rename to x-tba/slices/19-empty-file-finder-project/exercises/1-sort-to-a-file/solution/main.go
diff --git a/15-slices/exercises/11-append-5-sort-to-a-file/main.go b/x-tba/slices/19-empty-file-finder-project/exercises/2-sort-to-a-file-2/main.go
similarity index 95%
rename from 15-slices/exercises/11-append-5-sort-to-a-file/main.go
rename to x-tba/slices/19-empty-file-finder-project/exercises/2-sort-to-a-file-2/main.go
index 315e51b..84e7954 100644
--- a/15-slices/exercises/11-append-5-sort-to-a-file/main.go
+++ b/x-tba/slices/19-empty-file-finder-project/exercises/2-sort-to-a-file-2/main.go
@@ -8,7 +8,7 @@ import (
 )
 
 // ---------------------------------------------------------
-// EXERCISE: Append #5 — Sort to a file with ordinals
+// EXERCISE: Sort to a file with ordinals
 //
 //  Use the previous exercise: Append #4
 //
diff --git a/15-slices/exercises/11-append-5-sort-to-a-file/solution/main.go b/x-tba/slices/19-empty-file-finder-project/exercises/2-sort-to-a-file-2/solution/main.go
similarity index 100%
rename from 15-slices/exercises/11-append-5-sort-to-a-file/solution/main.go
rename to x-tba/slices/19-empty-file-finder-project/exercises/2-sort-to-a-file-2/solution/main.go
diff --git a/15-slices/exercises/12-append-6-print-directories/main.go b/x-tba/slices/19-empty-file-finder-project/exercises/3-print-directories/main.go
similarity index 96%
rename from 15-slices/exercises/12-append-6-print-directories/main.go
rename to x-tba/slices/19-empty-file-finder-project/exercises/3-print-directories/main.go
index 03a005e..11f3153 100644
--- a/15-slices/exercises/12-append-6-print-directories/main.go
+++ b/x-tba/slices/19-empty-file-finder-project/exercises/3-print-directories/main.go
@@ -1,7 +1,7 @@
 package main
 
 // ---------------------------------------------------------
-// EXERCISE: Append #6 — Print the directories
+// EXERCISE: Print the directories
 //
 //  Create a program that can get multiple directory paths from
 //  the command-line, and prints only their subdirectories into a
diff --git a/15-slices/exercises/12-append-6-print-directories/solution/dir/.gitignore b/x-tba/slices/19-empty-file-finder-project/exercises/3-print-directories/solution/dir/.gitignore
similarity index 100%
rename from 15-slices/exercises/12-append-6-print-directories/solution/dir/.gitignore
rename to x-tba/slices/19-empty-file-finder-project/exercises/3-print-directories/solution/dir/.gitignore
diff --git a/15-slices/exercises/12-append-6-print-directories/solution/dir/subdir1/.gitignore b/x-tba/slices/19-empty-file-finder-project/exercises/3-print-directories/solution/dir/subdir1/.gitignore
similarity index 100%
rename from 15-slices/exercises/12-append-6-print-directories/solution/dir/subdir1/.gitignore
rename to x-tba/slices/19-empty-file-finder-project/exercises/3-print-directories/solution/dir/subdir1/.gitignore
diff --git a/15-slices/exercises/12-append-6-print-directories/solution/dir/subdir2/.gitignore b/x-tba/slices/19-empty-file-finder-project/exercises/3-print-directories/solution/dir/subdir2/.gitignore
similarity index 100%
rename from 15-slices/exercises/12-append-6-print-directories/solution/dir/subdir2/.gitignore
rename to x-tba/slices/19-empty-file-finder-project/exercises/3-print-directories/solution/dir/subdir2/.gitignore
diff --git a/15-slices/exercises/12-append-6-print-directories/solution/dir2/.gitignore b/x-tba/slices/19-empty-file-finder-project/exercises/3-print-directories/solution/dir2/.gitignore
similarity index 100%
rename from 15-slices/exercises/12-append-6-print-directories/solution/dir2/.gitignore
rename to x-tba/slices/19-empty-file-finder-project/exercises/3-print-directories/solution/dir2/.gitignore
diff --git a/15-slices/exercises/12-append-6-print-directories/solution/dir2/subdir1/.gitignore b/x-tba/slices/19-empty-file-finder-project/exercises/3-print-directories/solution/dir2/subdir1/.gitignore
similarity index 100%
rename from 15-slices/exercises/12-append-6-print-directories/solution/dir2/subdir1/.gitignore
rename to x-tba/slices/19-empty-file-finder-project/exercises/3-print-directories/solution/dir2/subdir1/.gitignore
diff --git a/15-slices/exercises/12-append-6-print-directories/solution/dir2/subdir2/.gitignore b/x-tba/slices/19-empty-file-finder-project/exercises/3-print-directories/solution/dir2/subdir2/.gitignore
similarity index 100%
rename from 15-slices/exercises/12-append-6-print-directories/solution/dir2/subdir2/.gitignore
rename to x-tba/slices/19-empty-file-finder-project/exercises/3-print-directories/solution/dir2/subdir2/.gitignore
diff --git a/15-slices/exercises/12-append-6-print-directories/solution/dir2/subdir3/.gitignore b/x-tba/slices/19-empty-file-finder-project/exercises/3-print-directories/solution/dir2/subdir3/.gitignore
similarity index 100%
rename from 15-slices/exercises/12-append-6-print-directories/solution/dir2/subdir3/.gitignore
rename to x-tba/slices/19-empty-file-finder-project/exercises/3-print-directories/solution/dir2/subdir3/.gitignore
diff --git a/15-slices/exercises/12-append-6-print-directories/solution/dirs.txt b/x-tba/slices/19-empty-file-finder-project/exercises/3-print-directories/solution/dirs.txt
similarity index 100%
rename from 15-slices/exercises/12-append-6-print-directories/solution/dirs.txt
rename to x-tba/slices/19-empty-file-finder-project/exercises/3-print-directories/solution/dirs.txt
diff --git a/15-slices/exercises/12-append-6-print-directories/solution/main.go b/x-tba/slices/19-empty-file-finder-project/exercises/3-print-directories/solution/main.go
similarity index 100%
rename from 15-slices/exercises/12-append-6-print-directories/solution/main.go
rename to x-tba/slices/19-empty-file-finder-project/exercises/3-print-directories/solution/main.go
diff --git a/x-tba/slices/19-empty-file-finder-project/exercises/README.md b/x-tba/slices/19-empty-file-finder-project/exercises/README.md
new file mode 100644
index 0000000..942cec5
--- /dev/null
+++ b/x-tba/slices/19-empty-file-finder-project/exercises/README.md
@@ -0,0 +1,7 @@
+# File Append Exercises
+
+1. **[Sort and write items to a file](https://github.com/inancgumus/learngo/tree/master/15-slices/19-empty-file-finder-project/exercises/1-sort-to-a-file)**
+
+2. **[Sort and write items to a file with their ordinals](https://github.com/inancgumus/learngo/tree/master/15-slices/19-empty-file-finder-project/exercises/2-sort-to-a-file)**
+
+3. **[Find and write the names of subdirectories to a file](https://github.com/inancgumus/learngo/tree/master/15-slices/19-empty-file-finder-project/exercises/3-print-directories)**
\ No newline at end of file
diff --git a/x-tba/slices/13-png-parser/1-png-anatomy-format.md b/x-tba/slices/20-png-parser-project/1-png-anatomy-format.md
similarity index 59%
rename from x-tba/slices/13-png-parser/1-png-anatomy-format.md
rename to x-tba/slices/20-png-parser-project/1-png-anatomy-format.md
index 53eb0a8..52b10ee 100644
--- a/x-tba/slices/13-png-parser/1-png-anatomy-format.md
+++ b/x-tba/slices/20-png-parser-project/1-png-anatomy-format.md
@@ -4,14 +4,14 @@
 The first 24 bytes:
 
 +=================================+
-|  PNG Header         |  8 bytes  | -> 137 80 78 71 13 10 26 10
+|  PNG Header         |  8 bytes  | -> 89 50 4e 47 0d 0a 1a 0a
 +---------------------+-----------+
 |  IHDR Chunk Header  |           |
 |    Chunk Length     |  4 bytes  | -> The length of the IHDR Chunk Data
-|    Chunk Type       |  4 bytes  | -> 73 72 68 82
+|    Chunk Type       |  4 bytes  | -> 49 48 44 52
 +---------------------+-----------+
 |  IHDR Chunk Data    |           |
-|    Width            |  4 bytes  | -> Unsigned 32-bit integer
-|    Height           |  4 bytes  | -> Unsigned 32-bit integer
+|    Width            |  4 bytes  | -> uint32 — big endian
+|    Height           |  4 bytes  | -> uint32 — big endian
 +=================================+
 ```
\ No newline at end of file
diff --git a/x-tba/slices/20-png-parser-project/2-png-anatomy-example.md b/x-tba/slices/20-png-parser-project/2-png-anatomy-example.md
new file mode 100644
index 0000000..d6165e2
--- /dev/null
+++ b/x-tba/slices/20-png-parser-project/2-png-anatomy-example.md
@@ -0,0 +1,26 @@
+# The Brief Anatomy of a PNG image
+
+```
+The first 24 bytes:
+(all numbers are uint32 big-endian)
+
+PNG HEADER
+╔════╗╔════╗╔════╗╔════╗╔════╗╔════╗╔════╗╔════╗
+║ 89 ║║ 50 ║║ 4e ║║ 47 ║║ 0d ║║ 0a ║║ 1a ║║ 0a ║
+╚════╝╚════╝╚════╝╚════╝╚════╝╚════╝╚════╝╚════╝
+   0     1     2     3     4     5     6     7
+
+CHUNK LENGTH            CHUNK TYPE (IHDR)
+╔════╗╔════╗╔════╗╔════╗╔════╗╔════╗╔════╗╔════╗
+║ 00 ║║ 00 ║║ 00 ║║ 0d ║║ 49 ║║ 48 ║║ 44 ║║ 52 ║
+╚════╝╚════╝╚════╝╚════╝╚════╝╚════╝╚════╝╚════╝
+   8     9    10    11    12    13    14    15
+
+WIDTH                   HEIGHT
+╔════╗╔════╗╔════╗╔════╗╔════╗╔════╗╔════╗╔════╗
+║ 00 ║║ 00 ║║ 02 ║║ 4c ║║ 00 ║║ 00 ║║ 03 ║║ 20 ║
+╚════╝╚════╝╚════╝╚════╝╚════╝╚════╝╚════╝╚════╝
+  16    17    18    19    20    21    22    23
+
+... rest of the bytes in the png image ...
+```
\ No newline at end of file
diff --git a/x-tba/slices/13-png-parser/images/broken-missing-ihdr.png b/x-tba/slices/20-png-parser-project/images/broken-missing-ihdr.png
similarity index 100%
rename from x-tba/slices/13-png-parser/images/broken-missing-ihdr.png
rename to x-tba/slices/20-png-parser-project/images/broken-missing-ihdr.png
diff --git a/x-tba/slices/13-png-parser/images/broken-missing-png-header.png b/x-tba/slices/20-png-parser-project/images/broken-missing-png-header.png
similarity index 100%
rename from x-tba/slices/13-png-parser/images/broken-missing-png-header.png
rename to x-tba/slices/20-png-parser-project/images/broken-missing-png-header.png
diff --git a/x-tba/slices/13-png-parser/images/gopher.png b/x-tba/slices/20-png-parser-project/images/gopher.png
similarity index 100%
rename from x-tba/slices/13-png-parser/images/gopher.png
rename to x-tba/slices/20-png-parser-project/images/gopher.png
diff --git a/x-tba/slices/13-png-parser/main.go b/x-tba/slices/20-png-parser-project/main.go
similarity index 80%
rename from x-tba/slices/13-png-parser/main.go
rename to x-tba/slices/20-png-parser-project/main.go
index 6431060..ce91f6c 100644
--- a/x-tba/slices/13-png-parser/main.go
+++ b/x-tba/slices/20-png-parser-project/main.go
@@ -6,16 +6,10 @@ import (
 	"fmt"
 	"io/ioutil"
 	"os"
-
-	ps "github.com/inancgumus/prettyslice"
+	"runtime"
 )
 
 func main() {
-	var (
-		pngHeader     = [...]byte{137, 80, 78, 71, 13, 10, 26, 10}
-		ihdrChunkType = [...]byte{73, 72, 68, 82}
-	)
-
 	args := os.Args[1:]
 	if len(args) == 0 {
 		fmt.Println("run with a PNG file")
@@ -31,10 +25,19 @@ func main() {
 		return
 	}
 
-	// limit the capacity to prevent the errors downward
-	// 'cause we only need the first 24 bytes
+	img = append([]byte(nil), img[:24]...)
 	img = img[:24:24]
-	// ps.Show("first 24 bytes", img)
+
+	// s.PrintBacking = true
+	// s.MaxPerLine = 8
+	// s.MaxElements = 24
+	// s.PrintBytesHex = true
+	// s.Show("first 24 bytes", img)
+
+	var (
+		pngHeader     = [...]byte{0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a}
+		ihdrChunkType = [...]byte{0x49, 0x48, 0x44, 0x52}
+	)
 
 	// ------------------------------------------
 	// Read the PNG header
@@ -78,9 +81,9 @@ func main() {
 		binary.BigEndian.Uint32(ihdr[4:8]))
 }
 
-func init() {
-	ps.PrintBacking = true
-	ps.PrettyByteRune = false
-	ps.MaxPerLine = 8
-	ps.MaxElements = 32
+func report() {
+	var m runtime.MemStats
+	runtime.GC()
+	runtime.ReadMemStats(&m)
+	fmt.Printf(" > Memory Usage: %v KB\n", m.Alloc/1024)
 }
diff --git a/x-tba/slices/19-bouncing-ball-challenge/01-solution-draw-the-board/main.go b/x-tba/slices/21-bouncing-ball-project/01-solution-draw-the-board/main.go
similarity index 100%
rename from x-tba/slices/19-bouncing-ball-challenge/01-solution-draw-the-board/main.go
rename to x-tba/slices/21-bouncing-ball-project/01-solution-draw-the-board/main.go
diff --git a/x-tba/slices/19-bouncing-ball-challenge/02-solution-drawing-loop/main.go b/x-tba/slices/21-bouncing-ball-project/02-solution-drawing-loop/main.go
similarity index 100%
rename from x-tba/slices/19-bouncing-ball-challenge/02-solution-drawing-loop/main.go
rename to x-tba/slices/21-bouncing-ball-project/02-solution-drawing-loop/main.go
diff --git a/x-tba/slices/19-bouncing-ball-challenge/03-solution-final/main.go b/x-tba/slices/21-bouncing-ball-project/03-solution-final/main.go
similarity index 100%
rename from x-tba/slices/19-bouncing-ball-challenge/03-solution-final/main.go
rename to x-tba/slices/21-bouncing-ball-project/03-solution-final/main.go
diff --git a/x-tba/slices/19-bouncing-ball-challenge/04-solution-final-optimize/main.go b/x-tba/slices/21-bouncing-ball-project/04-solution-final-optimize/main.go
similarity index 100%
rename from x-tba/slices/19-bouncing-ball-challenge/04-solution-final-optimize/main.go
rename to x-tba/slices/21-bouncing-ball-project/04-solution-final-optimize/main.go
diff --git a/x-tba/slices/19-bouncing-ball-challenge/README.md b/x-tba/slices/21-bouncing-ball-project/README.md
similarity index 100%
rename from x-tba/slices/19-bouncing-ball-challenge/README.md
rename to x-tba/slices/21-bouncing-ball-project/README.md