diff --git a/ch1/server1/main.go b/ch1/server1/main.go
index 0bc7ce0..600e92c 100644
--- a/ch1/server1/main.go
+++ b/ch1/server1/main.go
@@ -18,7 +18,7 @@ func main() {
 	log.Fatal(http.ListenAndServe("localhost:8000", nil))
 }
 
-// handler echoes the Path component of the request URL r.
+// handler echoes the Path component of the requested URL.
 func handler(w http.ResponseWriter, r *http.Request) {
 	fmt.Fprintf(w, "URL.Path = %q\n", r.URL.Path)
 }
diff --git a/ch1/server3/main.go b/ch1/server3/main.go
index aa8316c..88c4ad5 100644
--- a/ch1/server3/main.go
+++ b/ch1/server3/main.go
@@ -2,24 +2,18 @@
 // License: https://creativecommons.org/licenses/by-nc-sa/4.0/
 
 // See page 21.
-//!+
 
-// Server3 is a minimal "echo" and counter server.
+// Server3 is an "echo" server that displays request parameters.
 package main
 
 import (
 	"fmt"
 	"log"
 	"net/http"
-	"sync"
 )
 
-var mu sync.Mutex
-var count int
-
 func main() {
 	http.HandleFunc("/", handler)
-	http.HandleFunc("/count", counter)
 	log.Fatal(http.ListenAndServe("localhost:8000", nil))
 }
 
@@ -41,12 +35,3 @@ func handler(w http.ResponseWriter, r *http.Request) {
 }
 
 //!-handler
-
-// counter echoes the number of calls so far.
-func counter(w http.ResponseWriter, r *http.Request) {
-	mu.Lock()
-	fmt.Fprintf(w, "Count %d", count)
-	mu.Unlock()
-}
-
-//!-
diff --git a/ch11/storage1/storage.go b/ch11/storage1/storage.go
index 9c2c81c..ed8982c 100644
--- a/ch11/storage1/storage.go
+++ b/ch11/storage1/storage.go
@@ -13,7 +13,9 @@ import (
 	"net/smtp"
 )
 
-func bytesInUse(username string) int64 { return 0 /* ... */ }
+var usage = make(map[string]int64)
+
+func bytesInUse(username string) int64 { return usage[username] }
 
 // Email sender configuration.
 // NOTE: never put passwords in source code!
diff --git a/ch11/storage2/quota_test.go b/ch11/storage2/quota_test.go
index 513a051..2dcd045 100644
--- a/ch11/storage2/quota_test.go
+++ b/ch11/storage2/quota_test.go
@@ -16,10 +16,7 @@ func TestCheckQuotaNotifiesUser(t *testing.T) {
 	}
 
 	const user = "joe@example.org"
-
-	// Simulate a 980MB-used condition for this user.
-	// NOTE: this differs slightly from the printed version.
-	usage["joe@example.org"] = 980000000
+	usage[user] = 980000000 // simulate a 980MB-used condition
 
 	CheckQuota(user)
 	if notifiedUser == "" && notifiedMsg == "" {
diff --git a/ch11/storage2/storage.go b/ch11/storage2/storage.go
index e9ca221..f103fbb 100644
--- a/ch11/storage2/storage.go
+++ b/ch11/storage2/storage.go
@@ -4,7 +4,6 @@
 // See page 312.
 
 // Package storage is part of a hypothetical cloud storage server.
-//!+main
 package storage
 
 import (
@@ -13,7 +12,6 @@ import (
 	"net/smtp"
 )
 
-// NOTE: this differs slightly from the printed version.
 var usage = make(map[string]int64)
 
 func bytesInUse(username string) int64 { return usage[username] }
diff --git a/ch3/printints/main.go b/ch3/printints/main.go
index 6dfa047..1c875d8 100644
--- a/ch3/printints/main.go
+++ b/ch3/printints/main.go
@@ -12,7 +12,7 @@ import (
 )
 
 //!+
-// intsToString is like fmt.Sprintf(values) but adds commas.
+// intsToString is like fmt.Sprint(values) but adds commas.
 func intsToString(values []int) string {
 	var buf bytes.Buffer
 	buf.WriteByte('[')
diff --git a/ch7/eval/print.go b/ch7/eval/print.go
index 1d3be26..69bf2db 100644
--- a/ch7/eval/print.go
+++ b/ch7/eval/print.go
@@ -1,8 +1,6 @@
 // Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
 // License: https://creativecommons.org/licenses/by-nc-sa/4.0/
 
-//+build ignore
-
 package eval
 
 import (
@@ -26,19 +24,19 @@ func write(buf *bytes.Buffer, e Expr) {
 	case Var:
 		fmt.Fprintf(buf, "%s", e)
 
-	case *unary:
+	case unary:
 		fmt.Fprintf(buf, "(%c", e.op)
 		write(buf, e.x)
 		buf.WriteByte(')')
 
-	case *binary:
+	case binary:
 		buf.WriteByte('(')
 		write(buf, e.x)
 		fmt.Fprintf(buf, " %c ", e.op)
 		write(buf, e.y)
 		buf.WriteByte(')')
 
-	case *call:
+	case call:
 		fmt.Fprintf(buf, "%s(", e.fn)
 		for i, arg := range e.args {
 			if i > 0 {
@@ -47,5 +45,8 @@ func write(buf *bytes.Buffer, e Expr) {
 			write(buf, arg)
 		}
 		buf.WriteByte(')')
+
+	default:
+		panic(fmt.Sprintf("unknown Expr: %T", e))
 	}
 }