= Solution
The output is \b[`YXWX`], without a newline. Apply <overload selection followed by dynamic dispatch> separately to each call:
* `c.m(a)` selects the `m(A)` signature because the argument's <static type> is `A`. The receiver is a `D` at runtime, so its override prints `Y`.
* `d.m(b)` selects `m(B)`. `D.m(B)` explicitly calls the inherited implementation with `super.m(o)`, giving `X`.
* `e.m(a)` selects `C.m(A)`, giving `W`.
* `e.m(b)` selects `C.m(B)`, giving `X`.
Although `a` actually refers to a `B`, that <runtime type> does not select another overload. <Dynamic dispatch> chooses the implementation of the already selected signature on the receiver.
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