major cleanup of tsig datastructures and extend/merge operations; fixes old bugs in classes/arities code; proper treatment of nonterminals and syntax-only types;
Chain = List +
consts chain :: "('a => 'a => bool) * 'a list => bool"
recdef chain "measure (%(r,xs). length xs)"
"chain(r, []) = True"
"chain(r, [x]) = True"
"chain(r, x#y#zs) = (r x y & chain(r, y#zs))"
end