public class A { public class B : A { public class A : B {} } }
Move class 'A.B.A' to outer scope. Set its name to 'C'.
public class A { public class B : C {} public class C : B {} // error CS0146: Circular base class dependency involving 'A.C' and 'A.B' }
Expected:
public class A { public class B : A {} public class C : B {} }