func (u *Union) String() string   { return TypeString(u, nil) }

// A Term represents a term in a Union.
type Term term

// NewTerm returns a new union term.
func NewTerm(tilde bool, typ Type) *Term { return &Term{tilde, typ} }

func (t *Term) Tilde() bool    { return t.tilde }
func (t *Term) Type() Type     { return t.typ }
func (t *Term) String() string { return (*term)(t).String() }

func _(x **********int) {
	h(x)
}

// Examples with channel constraints and tilde.

func ch1[P chan<- int]() (_ P)           { return } // core(P) == chan<- int   (single type, no tilde)
func ch2[P ~chan int]()                  { return } // core(P) == ~chan<- int  (tilde)
func ch3[P chan E, E any](E)             { return } // core(P) == chan<- E     (single type, no tilde)

func (u *Union) String() string   { return TypeString(u, nil) }

// A Term represents a term in a [Union].
type Term term

// NewTerm returns a new union term.
func NewTerm(tilde bool, typ Type) *Term { return &Term{tilde, typ} }

func (t *Term) Tilde() bool    { return t.tilde }
func (t *Term) Type() Type     { return t.typ }
func (t *Term) String() string { return (*term)(t).String() }

	//  T ⊆ ~t == true
	//  T ⊆  T == true
	return !x.tilde || y.tilde
}

// disjoint reports whether x ∩ y == ∅.
// x.typ and y.typ must not be nil.
func (x *term) disjoint(y *term) bool {
	if debug && (x.typ == nil || y.typ == nil) {
		panic("invalid argument(s)")
	}
	ux := x.typ
	if y.tilde {
		ux = under(ux)
	}
	uy := y.typ
	if x.tilde {
		uy = under(uy)
	}
	return !Identical(ux, uy)

	//  T ⊆ ~t == true
	//  T ⊆  T == true
	return !x.tilde || y.tilde
}

// disjoint reports whether x ∩ y == ∅.
// x.typ and y.typ must not be nil.
func (x *term) disjoint(y *term) bool {
	if debug && (x.typ == nil || y.typ == nil) {
		panic("invalid argument(s)")
	}
	ux := x.typ
	if y.tilde {
		ux = under(ux)
	}
	uy := y.typ
	if x.tilde {
		uy = under(uy)
	}
	return !Identical(ux, uy)

	//  T ⊆ ~t == true
	//  T ⊆  T == true
	return !x.tilde || y.tilde
}

// disjoint reports whether x ∩ y == ∅.
// x.typ and y.typ must not be nil.
func (x *term) disjoint(y *term) bool {
	if debug && (x.typ == nil || y.typ == nil) {
		panic("invalid argument(s)")
	}
	ux := x.typ
	if y.tilde {
		ux = under(ux)
	}
	uy := y.typ
	if x.tilde {
		uy = under(uy)
	}
	return !types.Identical(ux, uy)

        var m1 M1
        f(m1)
        g /* ERROR "M1 does not satisfy map[K]V" */ (m1) // M1 has tilde

        var m2 M2
        f(m2)
        g(m2) // M1 does not have tilde

        var m3 Map
        f(m3)
        g /* ERROR "Map does not satisfy map[string]int" */ (m3) // M in g does not have tilde

// term has a tilde. In all other cases coreTerm returns (nil, false).
func coreTerm(tpar *TypeParam) (*term, bool) {
	n := 0
	var single *term // valid if n == 1
	var tilde bool
	tpar.is(func(t *term) bool {
		if t == nil {
			assert(n == 0)
			return false // no terms
		}
		n++
		single = t
		if t.tilde {
			tilde = true
		}
		return true

// term has a tilde. In all other cases coreTerm returns (nil, false).
func coreTerm(tpar *TypeParam) (*term, bool) {
	n := 0
	var single *term // valid if n == 1
	var tilde bool
	tpar.is(func(t *term) bool {
		if t == nil {
			assert(n == 0)
			return false // no terms
		}
		n++
		single = t
		if t.tilde {
			tilde = true
		}
		return true

	INTERFACE
	MAP
	PACKAGE
	RANGE
	RETURN

	SELECT
	STRUCT
	SWITCH
	TYPE
	VAR
	keyword_end

	additional_beg
	// additional tokens, handled in an ad-hoc manner
	TILDE
	additional_end
)

var tokens = [...]string{
	ILLEGAL: "ILLEGAL",

	EOF:     "EOF",
	COMMENT: "COMMENT",

	IDENT:  "IDENT",
	INT:    "INT",
	FLOAT:  "FLOAT",
	IMAG:   "IMAG",