diff --git a/interfaces/08-composition/book.go b/interfaces/08-composition/book.go
index c583442..75fd437 100644
--- a/interfaces/08-composition/book.go
+++ b/interfaces/08-composition/book.go
@@ -8,19 +8,29 @@
 package main
 
 import (
+	"encoding/json"
 	"fmt"
 	"strconv"
 	"time"
 )
 
 type book struct {
-	*product
-	published interface{}
+	product
+	Published interface{}
 }
 
 func (b *book) String() string {
-	p := format(b.published)
-	return fmt.Sprintf("%s - (%v)", b.product, p)
+	p := format(b.Published)
+	return fmt.Sprintf("%s - (%v)", &b.product, p)
+}
+
+func (b *book) MarshalJSON() ([]byte, error) {
+	type jbook book
+
+	jb := (*jbook)(b)
+	jb.Published = format(b.Published)
+
+	return json.Marshal(jb)
 }
 
 func format(v interface{}) string {
diff --git a/interfaces/08-composition/game.go b/interfaces/08-composition/game.go
index 6811170..3604b15 100644
--- a/interfaces/08-composition/game.go
+++ b/interfaces/08-composition/game.go
@@ -8,5 +8,5 @@
 package main
 
 type game struct {
-	*product
+	product
 }
diff --git a/interfaces/08-composition/list.go b/interfaces/08-composition/list.go
index bd87c8c..2229250 100644
--- a/interfaces/08-composition/list.go
+++ b/interfaces/08-composition/list.go
@@ -12,12 +12,9 @@ import (
 	"strings"
 )
 
-type summer interface {
-	sum() money
-}
-
 type item interface {
-	summer       // same as: `sum() money`
+	sum() money
+	discount(float64)
 	fmt.Stringer // same as: `String() string`
 }
 
@@ -45,13 +42,7 @@ func (l list) sum() (total money) {
 }
 
 func (l list) discount(ratio float64) {
-	type discounter interface {
-		discount(float64)
-	}
-
 	for _, it := range l {
-		if it, ok := it.(discounter); ok {
-			it.discount(ratio)
-		}
+		it.discount(ratio)
 	}
 }
diff --git a/interfaces/08-composition/main.go b/interfaces/08-composition/main.go
index 606bc06..df022e2 100644
--- a/interfaces/08-composition/main.go
+++ b/interfaces/08-composition/main.go
@@ -8,35 +8,50 @@
 package main
 
 import (
+	"encoding/json"
 	"fmt"
 	"sort"
 )
 
 func main() {
 	store := list{
-		&book{&product{"moby dick", 10}, 118281600},
-		&book{&product{"odyssey", 15}, "733622400"},
-		&book{&product{"hobbit", 25}, nil},
-		&puzzle{&product{"rubik's cube", 5}},
-		&game{&product{"minecraft", 20}},
-		&game{&product{"tetris", 5}},
-		&toy{&product{"yoda", 150}},
+		&book{product{"moby dick", 10}, 118281600},
+		&book{product{"odyssey", 15}, "733622400"},
+		&book{product{"hobbit", 25}, nil},
+		&puzzle{product{"rubik's cube", 5}},
+		&game{product{"minecraft", 20}},
+		&game{product{"tetris", 5}},
+		&toy{product{"yoda", 150}},
 	}
 
+	out, _ := json.Marshal(store)
+	fmt.Println(string(out))
+
+	var (
+		nilItem item
+		nilBook *book
+	)
+
+	fmt.Println("nilBook     ?", nilBook == nil)
+	fmt.Println("nilItem?", nilItem == nil)
+
+	nilItem = nilBook
+	fmt.Println("nilItem?", nilItem == nil)
+
 	books := store[:3]
-	others := store[3:]
 
 	books.discount(.5)
 	fmt.Printf("%s\n", store)
 
+	others := store[3:]
 	sort.Sort(byPrice(others))
 	fmt.Printf("\n%s\n", store)
 
 	store = list{books, others}
 	fmt.Printf("\n%s\n", store)
 
-	// store.discount(.5)
-	// // sort.Sort(sort.Reverse(byPrice(store)))
-	// sort.Sort(byName(store))
-	// fmt.Println(store)
+	store.discount(.5)
+	// sort.Sort(sort.Reverse(byPrice(store)))
+	sort.Sort(byName(store))
+	fmt.Println(store)
 }
diff --git a/interfaces/08-composition/product.go b/interfaces/08-composition/product.go
index f1b3383..84e2ce6 100644
--- a/interfaces/08-composition/product.go
+++ b/interfaces/08-composition/product.go
@@ -10,18 +10,18 @@ package main
 import "fmt"
 
 type product struct {
-	title string
-	price money
+	Title string
+	Price money
 }
 
 func (p *product) discount(ratio float64) {
-	p.price *= money(1 - ratio)
+	p.Price *= money(1 - ratio)
 }
 
 func (p *product) sum() money {
-	return p.price
+	return p.Price
 }
 
 func (p *product) String() string {
-	return fmt.Sprintf("%-15s: %s", p.title, p.price)
+	return fmt.Sprintf("%-15s: %s", p.Title, p.Price)
 }
diff --git a/interfaces/08-composition/puzzle.go b/interfaces/08-composition/puzzle.go
index bf3ecc4..acbaa47 100644
--- a/interfaces/08-composition/puzzle.go
+++ b/interfaces/08-composition/puzzle.go
@@ -8,5 +8,5 @@
 package main
 
 type puzzle struct {
-	*product
+	product
 }
diff --git a/interfaces/08-composition/toy.go b/interfaces/08-composition/toy.go
index 73e99c4..ab5613d 100644
--- a/interfaces/08-composition/toy.go
+++ b/interfaces/08-composition/toy.go
@@ -8,5 +8,5 @@
 package main
 
 type toy struct {
-	*product
+	product
 }