diff --git a/LanguageFeatures/Enhanced-Enum/implementing_enum_A04_t25.dart b/LanguageFeatures/Enhanced-Enum/implementing_enum_A04_t25.dart
new file mode 100644
index 0000000..b621bb6
--- /dev/null
+++ b/LanguageFeatures/Enhanced-Enum/implementing_enum_A04_t25.dart
@@ -0,0 +1,49 @@
+// Copyright (c) 2022, 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 It’s currently a compile-time error for a class to implement,
+/// extend or mix-in the Enum class.
+///
+/// Because we want to allow interfaces and mixins that are intended to be
+/// applied to enum declarations, and therefore to assume Enum to be a
+/// superclass, we loosen that restriction to:
+/// ...
+/// It's a compile-time error if a class or mixin declaration has Enum as a
+/// superinterface, and that class or mixin declares or inherits a concrete
+/// instance member named `index`, `hashCode` or `==` (an `operator ==`
+/// declaration). That `index` member could override the `index` getter
+/// inherited from `Enum`, and we currently do not allow that. The `hashCode`
+/// and `operator ==` declarations would prevent the enum class from having
+/// "primitive equality", and we want to ensure that enums can be used in
+/// switches.
+///
+/// @description Check that it's a compile-time error if a class declaration has
+/// Enum as a superinterface, and it declares a non-abstract instance member
+/// named `operator ==`.
+/// @author sgrekhov@unipro.ru
+
+// SharedOptions=--enable-experiment=enhanced-enums
+
+abstract class E1 extends Enum {
+  bool operator ==(Object other) {
+//     ^^^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+    return true;
+  }
+}
+
+abstract class E2 extends Enum {
+  bool operator ==(covariant E2 other) {
+//     ^^^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+    return false;
+  }
+}
+
+main() {
+  print(E1);
+  print(E2);
+}
diff --git a/LanguageFeatures/Enhanced-Enum/implementing_enum_A04_t26.dart b/LanguageFeatures/Enhanced-Enum/implementing_enum_A04_t26.dart
new file mode 100644
index 0000000..b397111
--- /dev/null
+++ b/LanguageFeatures/Enhanced-Enum/implementing_enum_A04_t26.dart
@@ -0,0 +1,56 @@
+// Copyright (c) 2022, 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 It’s currently a compile-time error for a class to implement,
+/// extend or mix-in the Enum class.
+///
+/// Because we want to allow interfaces and mixins that are intended to be
+/// applied to enum declarations, and therefore to assume Enum to be a
+/// superclass, we loosen that restriction to:
+/// ...
+/// It's a compile-time error if a class or mixin declaration has Enum as a
+/// superinterface, and that class or mixin declares or inherits a concrete
+/// instance member named `index`, `hashCode` or `==` (an `operator ==`
+/// declaration). That `index` member could override the `index` getter
+/// inherited from `Enum`, and we currently do not allow that. The `hashCode`
+/// and `operator ==` declarations would prevent the enum class from having
+/// "primitive equality", and we want to ensure that enums can be used in
+/// switches.
+///
+/// @description Check that it's a compile-time error if an enum declaration has
+/// Enum as a superinterface, and it declares a non-abstract instance member
+/// named `operator ==`.
+/// @author sgrekhov@unipro.ru
+
+// SharedOptions=--enable-experiment=enhanced-enums
+
+enum E1 {
+  e1,
+  e2;
+
+  bool operator ==(Object other) {
+//     ^^^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+    return true;
+  }
+}
+
+enum E2 {
+  e1(42),
+  e2(0);
+
+  const E2(int i);
+  bool operator ==(covariant E2 other) {
+//    ^^^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+    return false;
+  }
+}
+
+main() {
+  print(E1);
+  print(E2);
+}
diff --git a/LanguageFeatures/Enhanced-Enum/implementing_enum_A04_t27.dart b/LanguageFeatures/Enhanced-Enum/implementing_enum_A04_t27.dart
new file mode 100644
index 0000000..c45e1cc
--- /dev/null
+++ b/LanguageFeatures/Enhanced-Enum/implementing_enum_A04_t27.dart
@@ -0,0 +1,49 @@
+// Copyright (c) 2022, 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 It’s currently a compile-time error for a class to implement,
+/// extend or mix-in the Enum class.
+///
+/// Because we want to allow interfaces and mixins that are intended to be
+/// applied to enum declarations, and therefore to assume Enum to be a
+/// superclass, we loosen that restriction to:
+/// ...
+/// It's a compile-time error if a class or mixin declaration has Enum as a
+/// superinterface, and that class or mixin declares or inherits a concrete
+/// instance member named `index`, `hashCode` or `==` (an `operator ==`
+/// declaration). That `index` member could override the `index` getter
+/// inherited from `Enum`, and we currently do not allow that. The `hashCode`
+/// and `operator ==` declarations would prevent the enum class from having
+/// "primitive equality", and we want to ensure that enums can be used in
+/// switches.
+///
+/// @description Check that it's a compile-time error if a mixin declaration has
+/// Enum as a superinterface, and it declares a non-abstract instance member
+/// named `operator ==`.
+/// @author sgrekhov@unipro.ru
+
+// SharedOptions=--enable-experiment=enhanced-enums
+
+mixin M1 on Enum {
+  bool operator ==(Object other) {
+//     ^^^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+    return true;
+  }
+}
+
+mixin M2 on Enum {
+  bool operator ==(covariant E2 other) {
+//    ^^^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+    return false;
+  }
+}
+
+main() {
+  print(M1);
+  print(M2);
+}