diff --git a/interfaces/11-sort/list.go b/interfaces/11-sort/list.go
index 69a9a85..722b337 100644
--- a/interfaces/11-sort/list.go
+++ b/interfaces/11-sort/list.go
@@ -21,8 +21,6 @@ func (l list) String() string {
 		return "Sorry. We're waiting for delivery 🚚.\n"
 	}
 
-	sort.Sort(l)
-
 	var str strings.Builder
 	for _, p := range l {
 		// fmt.Printf("* %s\n", p)
@@ -39,10 +37,12 @@ func (l list) discount(ratio float64) {
 	}
 }
 
+// implementation of the sort.Interface:
+
 // by default `list` sorts by `title`.
 func (l list) Len() int           { return len(l) }
-func (l list) Swap(i, j int)      { l[i], l[j] = l[j], l[i] }
 func (l list) Less(i, j int) bool { return l[i].title < l[j].title }
+func (l list) Swap(i, j int)      { l[i], l[j] = l[j], l[i] }
 
 // byRelease sorts by product release dates.
 type byRelease struct {
@@ -50,8 +50,20 @@ type byRelease struct {
 	list
 }
 
+// Less takes priority over the Less method of the `list`.
+// `sort.Sort` will first call this method instead of the `list`'s Less method.
 func (bp byRelease) Less(i, j int) bool {
-	// Before() accepts a time.Time but `released` is not time.Time.
-	// `released.Time` is necessary.
+	// `Before()` accepts a `time.Time` but `released` is not `time.Time`.
 	return bp.list[i].released.Before(bp.list[j].released.Time)
 }
+
+/*
+Anonymous embedding means auto-forwarding method calls to the embedded value:
+
+func (bp byRelease) Len() int      { return bp.list.Len() }
+func (bp byRelease) Swap(i, j int) { bp.list.Swap(i, j)   }
+*/
+
+func byReleaseDate(l list) sort.Interface {
+	return &byRelease{l}
+}
diff --git a/interfaces/11-sort/main.go b/interfaces/11-sort/main.go
index 3691fed..1ebb40d 100644
--- a/interfaces/11-sort/main.go
+++ b/interfaces/11-sort/main.go
@@ -9,7 +9,6 @@ package main
 
 import (
 	"fmt"
-	"sort"
 )
 
 func main() {
@@ -21,8 +20,27 @@ func main() {
 
 	// sort.Sort(l)
 	// sort.Sort(sort.Reverse(l))
-	// sort.Sort(byRelease{l})
-	sort.Sort(sort.Reverse(byRelease{l}))
+	// sort.Sort(byReleaseDate(l))
+	// sort.Sort(sort.Reverse(byReleaseDate(l)))
 
 	fmt.Print(l)
 }
+
+/*
+Summary:
+
+- sort.Sort() can sort any type that implements the sort.Interface
+
+- sort.Interface has three methods: Len(), Less(), Swap()
+  - Len() returns the length of a collection.
+  - Less() should return true when an element comes before another one.
+  - Swap()s the elements when Less() returns true.
+
+- sort.Reverse() sorts a sort.Interface value.
+
+- You can customize the sorting:
+  - by anonymously embedding the sort.Interface type
+  - and adding a Less() method.
+
+- Anonymous embedding means auto-forwarding method calls to an embedded value.
+*/
diff --git a/interfaces/12-marshaler/list.go b/interfaces/12-marshaler/list.go
index 018b629..b501e9f 100644
--- a/interfaces/12-marshaler/list.go
+++ b/interfaces/12-marshaler/list.go
@@ -8,7 +8,6 @@
 package main
 
 import (
-	"sort"
 	"strings"
 )
 
@@ -19,8 +18,6 @@ func (l list) String() string {
 		return "Sorry. We're waiting for delivery 🚚.\n"
 	}
 
-	sort.Sort(l)
-
 	var str strings.Builder
 	for _, p := range l {
 		// fmt.Printf("* %s\n", p)
diff --git a/interfaces/13-io/list.go b/interfaces/13-io/list.go
index 018b629..b501e9f 100644
--- a/interfaces/13-io/list.go
+++ b/interfaces/13-io/list.go
@@ -8,7 +8,6 @@
 package main
 
 import (
-	"sort"
 	"strings"
 )
 
@@ -19,8 +18,6 @@ func (l list) String() string {
 		return "Sorry. We're waiting for delivery 🚚.\n"
 	}
 
-	sort.Sort(l)
-
 	var str strings.Builder
 	for _, p := range l {
 		// fmt.Printf("* %s\n", p)
diff --git a/interfaces/14-composition/list.go b/interfaces/14-composition/list.go
index 018b629..b501e9f 100644
--- a/interfaces/14-composition/list.go
+++ b/interfaces/14-composition/list.go
@@ -8,7 +8,6 @@
 package main
 
 import (
-	"sort"
 	"strings"
 )
 
@@ -19,8 +18,6 @@ func (l list) String() string {
 		return "Sorry. We're waiting for delivery 🚚.\n"
 	}
 
-	sort.Sort(l)
-
 	var str strings.Builder
 	for _, p := range l {
 		// fmt.Printf("* %s\n", p)