extend: cleaned up, adapted for new Syntax.extend; extend, merge: improved roots (logical_types) handling;
extend: cleaned up, adapted for new Syntax.extend;
extend, merge: improved roots (logical_types) handling;

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