update_modesyntax: based on Syntax.update_const_gram (avoids duplicates);
update_modesyntax: based on Syntax.update_const_gram (avoids duplicates);

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