diff --git a/.github/workflows/go.yml b/.github/workflows/go.yml
index f470204..41a6185 100644
--- a/.github/workflows/go.yml
+++ b/.github/workflows/go.yml
@@ -12,7 +12,7 @@ jobs:
   test:
     strategy:
       matrix:
-        go-version: ['1.20']
+        go-version: ['1.21']
         os: [ubuntu-latest, macos-latest, windows-latest]
     runs-on: ${{ matrix.os }}
     steps:
@@ -27,7 +27,7 @@ jobs:
     steps:
       - uses: golang/govulncheck-action@v1
         with:
-          go-version-input: 1.20
+          go-version-input: 1.21
           check-latest: true
       
   coverage:
@@ -36,7 +36,7 @@ jobs:
       - uses: actions/checkout@v3         
       - uses: actions/setup-go@v4
         with:
-          go-version: 1.20
+          go-version: 1.21
 
       - name: Test Coverage
         run: go test -v -coverprofile=profile.cov ./...
@@ -51,7 +51,7 @@ jobs:
       - uses: actions/checkout@v3
       - uses: actions/setup-go@v4
         with:
-          go-version: 1.20
+          go-version: 1.21
           
       - name: golangci-lint
         uses: golangci/golangci-lint-action@v3
diff --git a/README.md b/README.md
index cd7d039..4a791c1 100644
--- a/README.md
+++ b/README.md
@@ -8,7 +8,7 @@
 
 ## API CHANGE !!!
 
-The API has changed from v0.1.0 to v0.2.0
+The API has changed from v0.9.1 to v0.10.0
 
 ## Overview
 
diff --git a/example_period_test.go b/example_period_test.go
index ceab64a..df7a45a 100644
--- a/example_period_test.go
+++ b/example_period_test.go
@@ -1,6 +1,7 @@
 package interval_test
 
 import (
+	"cmp"
 	"fmt"
 	"os"
 
@@ -12,18 +13,10 @@ type uintInterval [2]uint
 
 // cmp function for uintInterval
 func cmpUintInterval(p, q uintInterval) (ll, rr, lr, rl int) {
-	return cmpUint(p[0], q[0]), cmpUint(p[1], q[1]), cmpUint(p[0], q[1]), cmpUint(p[1], q[0])
-}
-
-// little helper
-func cmpUint(a, b uint) int {
-	switch {
-	case a == b:
-		return 0
-	case a < b:
-		return -1
-	}
-	return 1
+	return cmp.Compare(p[0], q[0]),
+		cmp.Compare(p[1], q[1]),
+		cmp.Compare(p[0], q[1]),
+		cmp.Compare(p[1], q[0])
 }
 
 // example data