var terms []*Term
		if !tp.is(func(t *term) bool {
			if t == nil {
				return false
			}
			if r := f(t.typ); r != nil {
				terms = append(terms, NewTerm(t.tilde, r))
				return true
			}
			return false
		}) {
			return nil
		}

		// We can type-check this fine but we're introducing a synthetic
		// type parameter for the result. It's not clear what the API

	// embed it in an implicit interface so that only interface type-checking
	// needs to take care of such type expressions.
	if op, _ := x.(*syntax.Operation); op != nil && (op.Op == syntax.Tilde || op.Op == syntax.Or) {
		t := check.typ(&syntax.InterfaceType{MethodList: []*syntax.Field{{Type: x}}})
		// mark t as implicit interface if all went well
		if t, _ := t.(*Interface); t != nil {
			t.implicit = true
		}

			} else {
				tok = s.switch3(token.AND, token.AND_ASSIGN, '&', token.LAND)
			}
		case '|':
			tok = s.switch3(token.OR, token.OR_ASSIGN, '|', token.LOR)
		case '~':
			tok = token.TILDE
		default:
			// next reports unexpected BOMs - don't repeat
			if ch != bom {
				// Report an informative error for U+201[CD] quotation
				// marks, which are easily introduced via copy and paste.

	{token.PERIOD, ".", operator},

	{token.RPAREN, ")", operator},
	{token.RBRACK, "]", operator},
	{token.RBRACE, "}", operator},
	{token.SEMICOLON, ";", operator},
	{token.COLON, ":", operator},
	{token.TILDE, "~", operator},

	// Keywords
	{token.BREAK, "break", keyword},
	{token.CASE, "case", keyword},
	{token.CHAN, "chan", keyword},
	{token.CONST, "const", keyword},
	{token.CONTINUE, "continue", keyword},

		var terms []*Term
		if !tp.is(func(t *term) bool {
			if t == nil {
				return false
			}
			if r := f(t.typ); r != nil {
				terms = append(terms, NewTerm(t.tilde, r))
				return true
			}
			return false
		}) {
			return nil
		}

		// We can type-check this fine but we're introducing a synthetic
		// type parameter for the result. It's not clear what the API

        entities.put("Scaron", "\u0160");
        entities.put("scaron", "\u0161");
        entities.put("Yuml", "\u0178");
        entities.put("circ", "\u02c6");
        entities.put("tilde", "\u02dc");
        entities.put("ensp", "\u2002");
        entities.put("emsp", "\u2003");
        entities.put("thinsp", "\u2009");
        entities.put("zwnj", "\u200c");
        entities.put("zwj", "\u200d");

	// embed it in an implicit interface so that only interface type-checking
	// needs to take care of such type expressions.
	wrap := false
	switch op := x.(type) {
	case *ast.UnaryExpr:
		wrap = op.Op == token.TILDE
	case *ast.BinaryExpr:
		wrap = op.Op == token.OR
	}
	if wrap {
		x = &ast.InterfaceType{Methods: &ast.FieldList{List: []*ast.Field{{Type: x}}}}
		t := check.typ(x)

			x.mode = invalid
			return
		}

		x.mode = commaok
		x.typ = ch.elem
		check.hasCallOrRecv = true
		return

	case token.TILDE:
		// Provide a better error position and message than what check.op below would do.
		if !allInteger(x.typ) {
			check.error(e, UndefinedOp, "cannot use ~ outside of interface or type constraint")
			x.mode = invalid

	"lt":       "\u003C",
	"gt":       "\u003E",
	"OElig":    "\u0152",
	"oelig":    "\u0153",
	"Scaron":   "\u0160",
	"scaron":   "\u0161",
	"Yuml":     "\u0178",
	"circ":     "\u02C6",
	"tilde":    "\u02DC",
	"ensp":     "\u2002",
	"emsp":     "\u2003",
	"thinsp":   "\u2009",
	"zwnj":     "\u200C",
	"zwj":      "\u200D",
	"lrm":      "\u200E",
	"rlm":      "\u200F",
	"ndash":    "\u2013",

			x.mode = invalid
			return
		}
		x.mode = commaok
		x.typ = ch.elem
		check.hasCallOrRecv = true
		return

	case syntax.Tilde:
		// Provide a better error position and message than what check.op below would do.
		if !allInteger(x.typ) {
			check.error(e, UndefinedOp, "cannot use ~ outside of interface or type constraint")
			x.mode = invalid