> if A is a subtype of B then List[A] should be considered a subtype of List[B] Well, careful -- I'm sure you know this by your name, but the naive treatment o

> if A is a subtype of B then List[A] should be considered a subtype of List[B] Well, careful -- I'm sure you know this by your name, but the naive treatment of Java's native array type as A[] <: B[] when A <: B leads to well-known soundness issues. Fundamentally that's because you can both read and write to Java's arrays; if you assume arrays are read-only then A[] <: B[] is indeed sound.