replace many uses of 'lemmas' with 'lemma'; remove many unused intermediate lemmas.
replace many uses of 'lemmas' with 'lemma';
remove many unused intermediate lemmas.

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