allow default values to refer to selector arguments -- this is useful, e.g. for tllist: ttl (TNil x) = TNil x (example by Andreas Lochbihler)
allow default values to refer to selector arguments -- this is useful, e.g. for tllist: ttl (TNil x) = TNil x (example by Andreas Lochbihler)

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