(* Title: Option.ML
ID: $Id$
Author: Tobias Nipkow
Copyright 1996 TU Muenchen
Derived rules
*)
open Option;
val [prem] = goal Option.thy "P(opt) ==> P(None) | (? x. P(Some(x)))";
br (prem RS rev_mp) 1;
by (option.induct_tac "opt" 1);
by (ALLGOALS(Fast_tac));
bind_thm("optionE", standard(result() RS disjE));
(*
goal Option.thy "opt=None | (? x.opt=Some(x))";
by (option.induct_tac "opt" 1);
by (Simp_tac 1);
by (rtac disjI2 1);
by (rtac exI 1);
by (Asm_full_simp_tac 1);
qed"option_cases";
*)
goal Option.thy "P(case opt of None => a | Some(x) => b(x)) = \
\ ((opt = None --> P a) & (!x. opt = Some x --> P(b(x))))";
by (option.induct_tac "opt" 1);
by (Simp_tac 1);
by (Asm_full_simp_tac 1);
by(Fast_tac 1);
qed"expand_option_case";