diff --git a/iface/01-iface.go b/iface/01-iface.go
deleted file mode 100644
index 4bb327b..0000000
--- a/iface/01-iface.go
+++ /dev/null
@@ -1,11 +0,0 @@
-package main
-
-type Strummer interface {
-	Strum()
-}
-
-type Bocchi struct {
-	Guitar string
-}
-
-var _ Strummer = (*Bocchi)(nil)
diff --git a/iface/chord.go b/iface/chord.go
new file mode 100644
index 0000000..cb6a444
--- /dev/null
+++ b/iface/chord.go
@@ -0,0 +1,3 @@
+package main
+
+type Chord string
diff --git a/iface/guitarist.go b/iface/guitarist.go
new file mode 100644
index 0000000..1983a7e
--- /dev/null
+++ b/iface/guitarist.go
@@ -0,0 +1,13 @@
+package main
+
+type Guitarist interface {
+	Strum(chord Chord)
+}
+
+type Bocchi struct {
+	Guitar string
+}
+
+func (b *Bocchi) Strum(chord string) {}
+
+var _ Guitarist = (*Bocchi)(nil)