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// Copyright (c) 2020, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
/// @assertion We say that a type T0 is a subtype of a type T1 (written T0 <: T1)
/// when:
/// Right Nullable: if T1 is S1? then:
/// T0 <: T1 iff any of the following hold:
/// either T0 <: S1
/// or T0 <: Null
/// or T0 is X0 and X0 has bound S0 and S0 <: T1
/// or T0 is X0 & S0 and S0 <: T1
/// @description Check that if type T1 is S1? and T0 is Null then T0 is subtype
/// of T1.
/// @author
class S1 {
const S1();
Null t0Instance = null;
S1? t1Instance = new S1();
const t1Default = const S1();
//# @T0 = Null
//# @T1 = S1?