cleaner, complete proof in documentation, contributed by Dmitriy T.
cleaner, complete proof in documentation, contributed by Dmitriy T.

MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle