diff --git a/src/cmd/cgo/gcc.go b/src/cmd/cgo/gcc.go
index 90f4032..1864eed 100644
--- a/src/cmd/cgo/gcc.go
+++ b/src/cmd/cgo/gcc.go
@@ -588,7 +588,7 @@
 				n.Const = strconv.Itoa64(n.Type.EnumValues[k])
 				// Remove injected enum to ensure the value will deep-compare
 				// equally in future loads of the same constant.
-				n.Type.EnumValues[k] = 0, false
+				delete(n.Type.EnumValues, k)
 			} else if n.Kind == "const" && i < len(enumVal) {
 				n.Const = strconv.Itoa64(enumVal[i])
 			}
diff --git a/src/cmd/gofmt/rewrite.go b/src/cmd/gofmt/rewrite.go
index 8f65ef1..7f2bf06 100644
--- a/src/cmd/gofmt/rewrite.go
+++ b/src/cmd/gofmt/rewrite.go
@@ -65,7 +65,7 @@
 			return reflect.Value{}
 		}
 		for k := range m {
-			m[k] = reflect.Value{}, false
+			delete(m, k)
 		}
 		val = apply(f, val)
 		if match(m, pat, val) {
diff --git a/src/pkg/debug/dwarf/type.go b/src/pkg/debug/dwarf/type.go
index f35365e..9fa221b 100644
--- a/src/pkg/debug/dwarf/type.go
+++ b/src/pkg/debug/dwarf/type.go
@@ -579,6 +579,6 @@
 	// If the parse fails, take the type out of the cache
 	// so that the next call with this offset doesn't hit
 	// the cache and return success.
-	d.typeCache[off] = nil, false
+	delete(d.typeCache, off)
 	return nil, err
 }
diff --git a/src/pkg/exp/types/check_test.go b/src/pkg/exp/types/check_test.go
index 8be653f..034acd0 100644
--- a/src/pkg/exp/types/check_test.go
+++ b/src/pkg/exp/types/check_test.go
@@ -154,7 +154,7 @@
 				continue
 			}
 			// we have a match - eliminate this error
-			expected[pos] = "", false
+			delete(expected, pos)
 		} else {
 			// To keep in mind when analyzing failed test output:
 			// If the same error position occurs multiple times in errors,
diff --git a/src/pkg/exp/types/universe.go b/src/pkg/exp/types/universe.go
index 6ae88e5..80db127 100644
--- a/src/pkg/exp/types/universe.go
+++ b/src/pkg/exp/types/universe.go
@@ -81,6 +81,7 @@
 	defFun("close")
 	defFun("complex")
 	defFun("copy")
+	defFun("delete")
 	defFun("imag")
 	defFun("len")
 	defFun("make")
diff --git a/src/pkg/gob/decode.go b/src/pkg/gob/decode.go
index 9d8d905..f480087 100644
--- a/src/pkg/gob/decode.go
+++ b/src/pkg/gob/decode.go
@@ -1154,7 +1154,7 @@
 		decoderMap[remoteId] = enginePtr
 		*enginePtr, err = dec.compileDec(remoteId, ut)
 		if err != nil {
-			decoderMap[remoteId] = nil, false
+			delete(decoderMap, remoteId)
 		}
 	}
 	return
@@ -1179,7 +1179,7 @@
 			*enginePtr, err = dec.compileIgnoreSingle(wireId)
 		}
 		if err != nil {
-			dec.ignorerCache[wireId] = nil, false
+			delete(dec.ignorerCache, wireId)
 		}
 	}
 	return
diff --git a/src/pkg/gob/type.go b/src/pkg/gob/type.go
index b2f716c..870101e 100644
--- a/src/pkg/gob/type.go
+++ b/src/pkg/gob/type.go
@@ -405,7 +405,7 @@
 	var type0, type1 gobType
 	defer func() {
 		if err != nil {
-			types[rt] = nil, false
+			delete(types, rt)
 		}
 	}()
 	// Install the top-level type before the subtypes (e.g. struct before
diff --git a/src/pkg/http/fcgi/child.go b/src/pkg/http/fcgi/child.go
index 1971882..61dd3fb 100644
--- a/src/pkg/http/fcgi/child.go
+++ b/src/pkg/http/fcgi/child.go
@@ -194,7 +194,7 @@
 		case typeData:
 			// If the filter role is implemented, read the data stream here.
 		case typeAbortRequest:
-			requests[rec.h.Id] = nil, false
+			delete(requests, rec.h.Id)
 			c.conn.writeEndRequest(rec.h.Id, 0, statusRequestComplete)
 			if !req.keepConn {
 				// connection will close upon return
diff --git a/src/pkg/http/persist.go b/src/pkg/http/persist.go
index 78bf905..f73e6c6 100644
--- a/src/pkg/http/persist.go
+++ b/src/pkg/http/persist.go
@@ -165,7 +165,7 @@
 	// Retrieve the pipeline ID of this request/response pair
 	sc.lk.Lock()
 	id, ok := sc.pipereq[req]
-	sc.pipereq[req] = 0, false
+	delete(sc.pipereq, req)
 	if !ok {
 		sc.lk.Unlock()
 		return ErrPipeline
@@ -353,7 +353,7 @@
 	// Retrieve the pipeline ID of this request/response pair
 	cc.lk.Lock()
 	id, ok := cc.pipereq[req]
-	cc.pipereq[req] = 0, false
+	delete(cc.pipereq, req)
 	if !ok {
 		cc.lk.Unlock()
 		return nil, ErrPipeline
diff --git a/src/pkg/http/transfer.go b/src/pkg/http/transfer.go
index 300c7a8..868a114 100644
--- a/src/pkg/http/transfer.go
+++ b/src/pkg/http/transfer.go
@@ -366,7 +366,7 @@
 		return nil, nil
 	}
 
-	header["Transfer-Encoding"] = nil, false
+	delete(header, "Transfer-Encoding")
 
 	// Head responses have no bodies, so the transfer encoding
 	// should be ignored.
@@ -399,7 +399,7 @@
 		// Chunked encoding trumps Content-Length. See RFC 2616
 		// Section 4.4. Currently len(te) > 0 implies chunked
 		// encoding.
-		header["Content-Length"] = nil, false
+		delete(header, "Content-Length")
 		return te, nil
 	}
 
diff --git a/src/pkg/http/transport.go b/src/pkg/http/transport.go
index b0aea97..0914af7 100644
--- a/src/pkg/http/transport.go
+++ b/src/pkg/http/transport.go
@@ -266,7 +266,7 @@
 		}
 		if len(pconns) == 1 {
 			pconn = pconns[0]
-			t.idleConn[key] = nil, false
+			delete(t.idleConn, key)
 		} else {
 			// 2 or more cached connections; pop last
 			// TODO: queue?
diff --git a/src/pkg/net/fd.go b/src/pkg/net/fd.go
index e46e120..80d40af 100644
--- a/src/pkg/net/fd.go
+++ b/src/pkg/net/fd.go
@@ -152,7 +152,7 @@
 	if !ok {
 		return nil
 	}
-	s.pending[key] = nil, false
+	delete(s.pending, key)
 	return netfd
 }
 
@@ -195,7 +195,7 @@
 		}
 		if t > 0 {
 			if t <= now {
-				s.pending[key] = nil, false
+				delete(s.pending, key)
 				if mode == 'r' {
 					s.poll.DelFD(fd.sysfd, mode)
 					fd.rdeadline = -1
diff --git a/src/pkg/net/fd_linux.go b/src/pkg/net/fd_linux.go
index 70fc344..c860c84 100644
--- a/src/pkg/net/fd_linux.go
+++ b/src/pkg/net/fd_linux.go
@@ -105,7 +105,7 @@
 		if e := syscall.EpollCtl(p.epfd, syscall.EPOLL_CTL_DEL, fd, nil); e != 0 {
 			print("Epoll delete fd=", fd, ": ", os.Errno(e).String(), "\n")
 		}
-		p.events[fd] = 0, false
+		delete(p.events, fd)
 	}
 }
 
diff --git a/src/pkg/net/textproto/header.go b/src/pkg/net/textproto/header.go
index 288deb2..7fb32f8 100644
--- a/src/pkg/net/textproto/header.go
+++ b/src/pkg/net/textproto/header.go
@@ -39,5 +39,5 @@
 
 // Del deletes the values associated with key.
 func (h MIMEHeader) Del(key string) {
-	h[CanonicalMIMEHeaderKey(key)] = nil, false
+	delete(h, CanonicalMIMEHeaderKey(key))
 }
diff --git a/src/pkg/net/textproto/pipeline.go b/src/pkg/net/textproto/pipeline.go
index 8c25884..ca50edd 100644
--- a/src/pkg/net/textproto/pipeline.go
+++ b/src/pkg/net/textproto/pipeline.go
@@ -108,7 +108,7 @@
 	}
 	c, ok := s.wait[id]
 	if ok {
-		s.wait[id] = nil, false
+		delete(s.wait, id)
 	}
 	s.mu.Unlock()
 	if ok {
diff --git a/src/pkg/old/netchan/export.go b/src/pkg/old/netchan/export.go
index 7df7365..99d5d7e 100644
--- a/src/pkg/old/netchan/export.go
+++ b/src/pkg/old/netchan/export.go
@@ -314,7 +314,7 @@
 // delClient forgets the client existed
 func (exp *Exporter) delClient(client *expClient) {
 	exp.mu.Lock()
-	exp.clients[client] = false, false
+	delete(exp.clients, client)
 	exp.mu.Unlock()
 }
 
@@ -388,7 +388,7 @@
 	exp.mu.Lock()
 	chDir, ok := exp.names[name]
 	if ok {
-		exp.names[name] = nil, false
+		delete(exp.names, name)
 	}
 	// TODO drop all instances of channel from client sets
 	exp.mu.Unlock()
diff --git a/src/pkg/old/netchan/import.go b/src/pkg/old/netchan/import.go
index ec17d97..5a459e0 100644
--- a/src/pkg/old/netchan/import.go
+++ b/src/pkg/old/netchan/import.go
@@ -256,8 +256,8 @@
 	if nc == nil {
 		return os.NewError("netchan import: hangup: no such channel: " + name)
 	}
-	imp.names[name] = nil, false
-	imp.chans[nc.id] = nil, false
+	delete(imp.names, name)
+	delete(imp.chans, nc.id)
 	nc.close()
 	return nil
 }
diff --git a/src/pkg/os/inotify/inotify_linux.go b/src/pkg/os/inotify/inotify_linux.go
index 99fa516..ee3c75f 100644
--- a/src/pkg/os/inotify/inotify_linux.go
+++ b/src/pkg/os/inotify/inotify_linux.go
@@ -131,7 +131,7 @@
 	if success == -1 {
 		return os.NewSyscallError("inotify_rm_watch", errno)
 	}
-	w.watches[path] = nil, false
+	delete(w.watches, path)
 	return nil
 }
 
diff --git a/src/pkg/reflect/type.go b/src/pkg/reflect/type.go
index 3630069..be5477d 100644
--- a/src/pkg/reflect/type.go
+++ b/src/pkg/reflect/type.go
@@ -876,7 +876,7 @@
 		fd = inf
 	}
 
-	mark[t] = false, false
+	delete(mark, t)
 	return
 }
 
diff --git a/src/pkg/rpc/client.go b/src/pkg/rpc/client.go
index 4acfdf6..c77901c 100644
--- a/src/pkg/rpc/client.go
+++ b/src/pkg/rpc/client.go
@@ -104,7 +104,7 @@
 		seq := response.Seq
 		client.mutex.Lock()
 		c := client.pending[seq]
-		client.pending[seq] = c, false
+		delete(client.pending, seq)
 		client.mutex.Unlock()
 
 		if response.Error == "" {
diff --git a/src/pkg/rpc/jsonrpc/client.go b/src/pkg/rpc/jsonrpc/client.go
index 577d0ce..17e9b93 100644
--- a/src/pkg/rpc/jsonrpc/client.go
+++ b/src/pkg/rpc/jsonrpc/client.go
@@ -79,7 +79,7 @@
 
 	c.mutex.Lock()
 	r.ServiceMethod = c.pending[c.resp.Id]
-	c.pending[c.resp.Id] = "", false
+	delete(c.pending, c.resp.Id)
 	c.mutex.Unlock()
 
 	r.Error = ""
diff --git a/src/pkg/rpc/jsonrpc/server.go b/src/pkg/rpc/jsonrpc/server.go
index 9801fdf..61b5abf 100644
--- a/src/pkg/rpc/jsonrpc/server.go
+++ b/src/pkg/rpc/jsonrpc/server.go
@@ -107,7 +107,7 @@
 		c.mutex.Unlock()
 		return os.NewError("invalid sequence number in response")
 	}
-	c.pending[r.Seq] = nil, false
+	delete(c.pending, r.Seq)
 	c.mutex.Unlock()
 
 	if b == nil {
diff --git a/src/pkg/syscall/syscall_unix.go b/src/pkg/syscall/syscall_unix.go
index 1590b6d..70ea3bd 100644
--- a/src/pkg/syscall/syscall_unix.go
+++ b/src/pkg/syscall/syscall_unix.go
@@ -87,6 +87,6 @@
 	if errno := m.munmap(uintptr(unsafe.Pointer(&b[0])), uintptr(len(b))); errno != 0 {
 		return errno
 	}
-	m.active[p] = nil, false
+	delete(m.active, p)
 	return 0
 }
diff --git a/src/pkg/unicode/maketables.go b/src/pkg/unicode/maketables.go
index 087422d..15579aa 100644
--- a/src/pkg/unicode/maketables.go
+++ b/src/pkg/unicode/maketables.go
@@ -1152,7 +1152,7 @@
 
 	// Remove class itself.
 	for _, r := range class {
-		m[r] = false, false
+		delete(m, r)
 	}
 
 	// What's left is the exceptions.
diff --git a/src/pkg/unicode/script_test.go b/src/pkg/unicode/script_test.go
index b37ad18..dfd636d 100644
--- a/src/pkg/unicode/script_test.go
+++ b/src/pkg/unicode/script_test.go
@@ -206,7 +206,7 @@
 		if !Is(Scripts[test.script], test.rune) {
 			t.Errorf("IsScript(%U, %s) = false, want true", test.rune, test.script)
 		}
-		notTested[test.script] = false, false
+		delete(notTested, test.script)
 	}
 	for _, test := range outTest {
 		if Is(Scripts[test.script], test.rune) {
@@ -230,7 +230,7 @@
 		if !Is(Categories[test.script], test.rune) {
 			t.Errorf("IsCategory(%U, %s) = false, want true", test.rune, test.script)
 		}
-		notTested[test.script] = false, false
+		delete(notTested, test.script)
 	}
 	for k := range notTested {
 		t.Error("category not tested:", k)
@@ -249,7 +249,7 @@
 		if !Is(Properties[test.script], test.rune) {
 			t.Errorf("IsCategory(%U, %s) = false, want true", test.rune, test.script)
 		}
-		notTested[test.script] = false, false
+		delete(notTested, test.script)
 	}
 	for k := range notTested {
 		t.Error("property not tested:", k)
diff --git a/src/pkg/url/url.go b/src/pkg/url/url.go
index 9d19348..dd1f93d 100644
--- a/src/pkg/url/url.go
+++ b/src/pkg/url/url.go
@@ -517,7 +517,7 @@
 
 // Del deletes the values associated with key.
 func (v Values) Del(key string) {
-	v[key] = nil, false
+	delete(v, key)
 }
 
 // ParseQuery parses the URL-encoded query string and returns
diff --git a/src/pkg/xml/xml.go b/src/pkg/xml/xml.go
index e7ba44e..85c24bc 100644
--- a/src/pkg/xml/xml.go
+++ b/src/pkg/xml/xml.go
@@ -390,7 +390,11 @@
 	// translations that were associated with the element we just closed.
 	for p.stk != nil && p.stk.kind != stkStart {
 		s := p.pop()
-		p.ns[s.name.Local] = s.name.Space, s.ok
+		if s.ok {
+			p.ns[s.name.Local] = s.name.Space
+		} else {
+			delete(p.ns, s.name.Local)
+		}
 	}
 
 	return true