unset_then_multiple_subgoals : (preprocessor keyword)

SYNOPSIS

Updates the HOL Light preprocessor to read THEN as an alternative operator which fails if the first tactic creates more than one subgoal.

DESCRIPTION

If a preprocessor reads unset_then_multiple_subgoals, it starts to translate t1 THEN t2 into then1_ t1 t2 which fails when t1 generates more than one subgoal. This is useful when one wants to check whether a proof written using THEN can be syntactically converted to the `e`-`g` form. If this setting is on, t1 THEN t2 THEN .. and e(t1);; e(t2);; ... have the same meaning (modulo the validity check). After preprocessing, unset_then_multiple_subgoals is identical to the false constant in OCaml. To roll back the behavior of THEN, use set_then_multiple_subgoals, which is identical to true modulo its side effect. This command is only available for OCaml 4.xx and above.

EXAMPLE

  # prove(`x + 1 = 1 + x /\ x + 2 = 2 + x`, CONJ_TAC THEN ARITH_TAC);;
  val it : thm = |- x + 1 = 1 + x /\ x + 2 = 2 + x

  # unset_then_multiple_subgoals;;
  val it : bool = false
  # prove(`x + 1 = 1 + x /\ x + 2 = 2 + x`, CONJ_TAC THEN ARITH_TAC);;
  Exception: Failure "seqapply: Length mismatch".
  # prove(`x + 1 = 1 + x /\ x + 2 = 2 + x`, CONJ_TAC THENL [ARITH_TAC; ARITH_TAC]);;
  val it : thm = |- x + 1 = 1 + x /\ x + 2 = 2 + x
  # prove(`x + 1 = 1 + x /\ x + 2 = 2 + x`, CONJ_TAC THENL (replicate ARITH_TAC 2));;
  val it : thm = |- x + 1 = 1 + x /\ x + 2 = 2 + x

FAILURE CONDITIONS

Never fails.

SEE ALSO

e, er, THEN, VALID.