major cleanup of tsig datastructures and extend/merge operations; fixes old bugs in classes/arities code; proper treatment of nonterminals and syntax-only types;
Goal "!xs. linInfixList t xs = infixList t @ xs";
by(induct_tac "t" 1);
by(Simp_tac 1);
by(Asm_simp_tac 1);