revert this idea of automatically invoking "metisFT" when "metis" fails;
there are very few good reasons why "metisFT" should succeed when "metis" fails, and "metisFT" tends to "diverge" more often than "metis -- furthermore the exception handling code wasn't working properly
Isabelle's Object-Logics. Report 286.
This is the third of the Isabelle manuals. It covers Isabelle's built-in
object logics: first-order logic (FOL), Zermelo-Fraenkel set theory (ZF),
higher-order logic (HOL), the classical sequent calculus (LK), and
constructive type theory (CTT). The final chapter discusses how to define
new logics. This manual assumes familiarity with Report 280, Introduction
to Isabelle.