Added "merge-lemma" about wellfoundedness of unions (useful for some termination proofs)
Added "merge-lemma" about wellfoundedness of unions (useful for some termination proofs)

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