diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..43937e7
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+*.html
+*.out
\ No newline at end of file
diff --git a/README.md b/README.md
index 7e8c6b3..2e56f1c 100644
--- a/README.md
+++ b/README.md
@@ -14,7 +14,15 @@ Once you have [installed Go][golang-install], run this command
 to install the `bit` package:
 
     go get github.com/yourbasic/bit
-    
+
+### Testing
+
+    go test -v -coverprofile coverage.out && go tool cover -html coverage.out -o coverage.html
+
+### Benchmarking
+
+    go test -bench . -benchmem -cpu 1
+
 ### Documentation
 
 There is an online reference for the package at
diff --git a/example_test.go b/example_test.go
index 6381f6f..88b69b5 100644
--- a/example_test.go
+++ b/example_test.go
@@ -2,8 +2,9 @@ package bit_test
 
 import (
 	"fmt"
-	"github.com/yourbasic/bit"
 	"math"
+
+	"github.com/yourbasic/bit"
 )
 
 // Create, combine, compare and print bit sets.
@@ -25,7 +26,12 @@ func Example_basics() {
 	if X.Equal(Y) {
 		fmt.Println(X)
 	}
+
+	// Compute A ∩ B
+	Z := A.And(B)
+	fmt.Println(Z)
 	// Output: {1..49 100..149 200}
+	// {0 50..99}
 }
 
 // Create the set of all primes less than n in O(n log log n) time.
diff --git a/example_union_test.go b/example_union_test.go
index 5de52f8..80743a9 100644
--- a/example_union_test.go
+++ b/example_union_test.go
@@ -2,6 +2,7 @@ package bit_test
 
 import (
 	"fmt"
+
 	"github.com/yourbasic/bit"
 )
 
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..efd5d38
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,3 @@
+module github.com/yourbasic/bit
+
+go 1.9
diff --git a/set.go b/set.go
index 0abebcb..1a539c6 100644
--- a/set.go
+++ b/set.go
@@ -1,15 +1,16 @@
+//go:build !go1.9
 // +build !go1.9
 
 // Package bit provides a bit array implementation.
 //
-// Bit set
+// # Bit set
 //
 // A bit set, or bit array, is an efficient set data structure
 // that consists of an array of 64-bit words. Because it uses
 // bit-level parallelism, limits memory access, and efficiently uses
 // the data cache, a bit set often outperforms other data structures.
 //
-// Tutorial
+// # Tutorial
 //
 // The Basics example shows how to create, combine, compare and
 // print bit sets.
@@ -19,7 +20,6 @@
 //
 // Union is a more advanced example demonstrating how to build
 // an efficient variadic Union function using the SetOr method.
-//
 package bit
 
 import (
diff --git a/set_1_10.go b/set_1_10.go
index 0dfd3c6..af3189f 100644
--- a/set_1_10.go
+++ b/set_1_10.go
@@ -1,15 +1,16 @@
+//go:build go1.10
 // +build go1.10
 
 // Package bit provides a bit array implementation.
 //
-// Bit set
+// # Bit set
 //
 // A bit set, or bit array, is an efficient set data structure
 // that consists of an array of 64-bit words. Because it uses
 // bit-level parallelism, limits memory access, and efficiently uses
 // the data cache, a bit set often outperforms other data structures.
 //
-// Tutorial
+// # Tutorial
 //
 // The Basics example shows how to create, combine, compare and
 // print bit sets.
@@ -19,7 +20,6 @@
 //
 // Union is a more advanced example demonstrating how to build
 // an efficient variadic Union function using the SetOr method.
-//
 package bit
 
 import (
diff --git a/set_1_9.go b/set_1_9.go
index 70e5f07..797c41a 100644
--- a/set_1_9.go
+++ b/set_1_9.go
@@ -1,16 +1,16 @@
-// +build go1.9
-// +build !go1.10
+//go:build go1.9 && !go1.10
+// +build go1.9,!go1.10
 
 // Package bit provides a bit array implementation.
 //
-// Bit set
+// # Bit set
 //
 // A bit set, or bit array, is an efficient set data structure
 // that consists of an array of 64-bit words. Because it uses
 // bit-level parallelism, limits memory access, and efficiently uses
 // the data cache, a bit set often outperforms other data structures.
 //
-// Tutorial
+// # Tutorial
 //
 // The Basics example shows how to create, combine, compare and
 // print bit sets.
@@ -20,7 +20,6 @@
 //
 // Union is a more advanced example demonstrating how to build
 // an efficient variadic Union function using the SetOr method.
-//
 package bit
 
 import (
diff --git a/set_test.go b/set_test.go
index 755909b..475eb88 100644
--- a/set_test.go
+++ b/set_test.go
@@ -299,11 +299,11 @@ func TestVisit(t *testing.T) {
 			t.Errorf("%v.Visit(func(n int) { s.DeleteRange(0, n+1); s += Itoa(n) }) -> s=%q; want %q", s, res, x.res)
 		}
 	}
-	s := New(1, 2)
+	s := New(1, 2, 3)
 	count := 0
 	aborted := s.Visit(func(n int) (skip bool) {
 		count++
-		if n == 1 {
+		if n == 2 {
 			skip = true
 			return
 		}
@@ -312,7 +312,7 @@ func TestVisit(t *testing.T) {
 	if aborted == false {
 		t.Errorf("Visit returned false when aborted.")
 	}
-	if count > 1 {
+	if count > 2 {
 		t.Errorf("Visit didn't abort.")
 	}
 	count = 0
@@ -323,7 +323,7 @@ func TestVisit(t *testing.T) {
 	if aborted == true {
 		t.Errorf("Visit returned true when not aborted.")
 	}
-	if count != 2 {
+	if count != 3 {
 		t.Errorf("Visit aborted.")
 	}
 }