diff --git a/x-tba/slices/11-slice-internals-3-len-cap/1-theory/main.go b/x-tba/slices/11-slice-internals-3-len-cap/1-theory/main.go
deleted file mode 100644
index e6b3506..0000000
--- a/x-tba/slices/11-slice-internals-3-len-cap/1-theory/main.go
+++ /dev/null
@@ -1,31 +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() {
-	s.MaxPerLine = 6
-	s.PrintBacking = true
-
-	ages := []int{35, 15, 25}
-	s.Show("ages", ages)
-
-	s.Show("ages[0:0]", ages[0:0])
-
-	for i := 1; i < 4; i++ {
-		txt := fmt.Sprintf("ages[%d:%d]", 0, i)
-		s.Show(txt, ages[0:i])
-	}
-
-	s.Show("append", append(ages, 50))
-}
diff --git a/x-tba/slices/11-slice-internals-3-len-cap/2-example/main.go b/x-tba/slices/11-slice-internals-3-len-cap/2-example/main.go
deleted file mode 100644
index 7c43578..0000000
--- a/x-tba/slices/11-slice-internals-3-len-cap/2-example/main.go
+++ /dev/null
@@ -1,56 +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() {
-	s.PrintBacking = true
-
-	// ----------------------------------------------------
-	// #1 nil slice
-	var games []string // nil slice
-	s.Show("games", games)
-
-	// ----------------------------------------------------
-	// #2 empty slice
-	games = []string{} // empty slice
-	s.Show("games", games)
-	// s.Show("another empty", []int{})
-
-	// ----------------------------------------------------
-	// #3 non-empty slice
-	games = []string{"pacman", "mario", "tetris", "doom"}
-	s.Show("games", games)
-
-	// ----------------------------------------------------
-	// #4 reset the part using the games slice
-	//    part is empty but its cap is still 4
-	part := games
-	s.Show("part", part)
-
-	part = games[:0]
-	s.Show("part[:0]", part)
-	s.Show("part[:cap]", part[:cap(part)])
-
-	for cap(part) != 0 {
-		part = part[1:cap(part)]
-		s.Show("part", part)
-	}
-
-	// #6 backing array's elements become inaccessible
-	// games = games[len(games):]
-
-	// ----------------------------------------------------
-	// #5 part doesn't have any more capacity
-	//    games slice is still intact
-	s.Show("part", part)
-	s.Show("games", games)
-}
diff --git a/x-tba/slices/12-slice-internals-4-append/1-theory/main.go b/x-tba/slices/12-slice-internals-4-append/1-theory/main.go
deleted file mode 100644
index 7386edb..0000000
--- a/x-tba/slices/12-slice-internals-4-append/1-theory/main.go
+++ /dev/null
@@ -1,22 +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() {
-	s.PrintBacking = true
-
-	ages := []int{35, 15}
-	s.Show("ages", ages)
-
-	ages = append(ages, 5)
-	s.Show("append(ages, 5)", ages)
-}
diff --git a/x-tba/slices/12-slice-internals-4-append/2-example/main.go b/x-tba/slices/12-slice-internals-4-append/2-example/main.go
deleted file mode 100644
index 11a1125..0000000
--- a/x-tba/slices/12-slice-internals-4-append/2-example/main.go
+++ /dev/null
@@ -1,54 +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() {
-	s.PrintBacking = true
-
-	// #1: a nil slice has no backing array
-	var nums []int
-	s.Show("no backing array", nums)
-
-	// #2: creates a new backing array
-	nums = append(nums, 1, 3)
-	s.Show("allocates", nums)
-
-	// #3: creates a new backing array
-	nums = append(nums, 2)
-	s.Show("free capacity", nums)
-
-	// #4: uses the same backing array
-	nums = append(nums, 4)
-	s.Show("no allocation", nums)
-
-	// GOAL: append new odd numbers in the middle
-	// [1 3 2 4] -> [1 3 7 9 2 4]
-
-	// #6: [1 3 2 4] -> [1 3 2 4 2 4]
-	nums = append(nums, nums[2:]...)
-	s.Show("nums <- nums[2:]", nums)
-
-	// #5: overwrites: [1 3 2 4 2 4] -> [1 3 7 9]
-	nums = append(nums[:2], 7, 9)
-	s.Show("nums[:2] <- 7, 9", nums)
-
-	// #7: [1 3 7 9] -> [1 3 7 9 2 4]
-	nums = nums[:6]
-	s.Show("nums: extend", nums)
-}
-
-// don't mind about these options
-// they're just for printing the slices nicely
-func init() {
-	s.MaxPerLine = 10
-	s.Width = 45
-}
diff --git a/x-tba/slices/12-slice-internals-4-append/3-example-growth/main.go b/x-tba/slices/12-slice-internals-4-append/3-example-growth/main.go
deleted file mode 100644
index 1df92ff..0000000
--- a/x-tba/slices/12-slice-internals-4-append/3-example-growth/main.go
+++ /dev/null
@@ -1,34 +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 (
-	"math/rand"
-	"time"
-
-	s "github.com/inancgumus/prettyslice"
-	"github.com/inancgumus/screen"
-)
-
-func main() {
-	s.PrintBacking = true
-	s.MaxPerLine = 30
-	s.Width = 150
-
-	var nums []int
-
-	screen.Clear()
-	for cap(nums) <= 128 {
-		screen.MoveTopLeft()
-
-		s.Show("nums", nums)
-		nums = append(nums, rand.Intn(9)+1)
-
-		time.Sleep(time.Second / 4)
-	}
-}
diff --git a/x-tba/slices/12-slice-internals-4-append/4-example-growth/main.go b/x-tba/slices/12-slice-internals-4-append/4-example-growth/main.go
deleted file mode 100644
index 94b7c1a..0000000
--- a/x-tba/slices/12-slice-internals-4-append/4-example-growth/main.go
+++ /dev/null
@@ -1,27 +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"
-)
-
-func main() {
-	ages, oldCap := []int{1}, 1.
-
-	for len(ages) < 5e5 {
-		ages = append(ages, 1)
-
-		c := float64(cap(ages))
-		if c != oldCap {
-			fmt.Printf("len:%-10d cap:%-10g growth:%.2f\n",
-				len(ages), c, c/oldCap)
-		}
-		oldCap = c
-	}
-}