improved error output -- variant/mark bounds; simplified infer_types -- always freeze, no result substitution;
improved error output -- variant/mark bounds;
simplified infer_types -- always freeze, no result substitution;

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