"~int | myInt":  false,
		"∅ | ∅ | 𝓤":     true,
		"𝓤":             true,
		"𝓤 | int":       true,
		"myInt | 𝓤":     true,
	} {
		xl := maketl(test)
		got := xl.isAll()
		if got != want {
			t.Errorf("(%v).isAll() == %v; want %v", test, got, want)
		}
	}
}

func TestTermlistNorm(t *testing.T) {
	for _, test := range []struct {
		xl, want string
	}{
		{"∅", "∅"},
		{"∅ | ∅", "∅"},

	// one iteration.
	for _, x := range xl {
		if x != nil {
			return false
		}
	}
	return true
}

// isAll reports whether the termlist xl represents the set of all types.
func (xl termlist) isAll() bool {
	// If there's a 𝓤 term, the entire list is 𝓤.
	// If the termlist is in normal form, this requires at most
	// one iteration.
	for _, x := range xl {