var maxUntyped map[*TypeParam]Type // lazily allocated (we may not need it)
	for _, index := range untyped {
		tpar := params.At(index).typ.(*TypeParam) // is type parameter (no alias) by construction of untyped
		if u.at(tpar) == nil {
			arg := args[index] // arg corresponding to tpar
			if maxUntyped == nil {
				maxUntyped = make(map[*TypeParam]Type)
			}
			max := maxUntyped[tpar]

	var maxUntyped map[*TypeParam]Type // lazily allocated (we may not need it)
	for _, index := range untyped {
		tpar := params.At(index).typ.(*TypeParam) // is type parameter (no alias) by construction of untyped
		if u.at(tpar) == nil {
			arg := args[index] // arg corresponding to tpar
			if maxUntyped == nil {
				maxUntyped = make(map[*TypeParam]Type)
			}
			max := maxUntyped[tpar]

	if !force {
		return l, r
	}

	// Can't mix nil with anything untyped.
	if ir.IsNil(l) || ir.IsNil(r) {
		return l, r
	}
	t := defaultType(mixUntyped(l.Type(), r.Type()))
	l = convlit(l, t)
	r = convlit(r, t)
	return l, r
}

func mixUntyped(t1, t2 *types.Type) *types.Type {
	if t1 == t2 {
		return t1
	}

	rank := func(t *types.Type) int {
		switch t {
		case types.UntypedInt:

			base.Errorf("invalid operation: %v (mismatched types %v and %v)", n, l.Type(), r.Type())
			return l, r, nil
		}
	}

	if t.Kind() == types.TIDEAL {
		t = mixUntyped(l.Type(), r.Type())
	}
	if dt := defaultType(t); !okfor[op][dt.Kind()] {
		base.Errorf("invalid operation: %v (operator %v not defined on %s)", n, op, typekind(t))
		return l, r, nil
	}