File: FIRST_ASSUM.doc

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\DOC FIRST_ASSUM

\TYPE {FIRST_ASSUM : thm_tactic -> tactic}

\SYNOPSIS
Applied theorem-tactic to first assumption possible.

\KEYWORDS
theorem-tactical, assumption.

\DESCRIBE
The tactic
{
   FIRST_ASSUM ttac ([A1; ...; An], g)
}
\noindent has the effect of applying the first tactic which can be produced by
{ttac} from the assumptions {(.. |- A1)}, ..., {(.. |- An)} and which
succeeds when applied to the goal. Failures of {ttac} to produce a tactic are
ignored. The similar function {FIRST_X_ASSUM} is the same except that the 
assumption used is then removed from the goal.

\FAILURE
Fails if {ttac (.. |- Ai)} fails for every assumption {Ai}, or if the
assumption list is empty, or if all the tactics produced by {ttac} fail when
applied to the goal.

\EXAMPLE
The tactic
{
   FIRST_ASSUM (fun asm -> CONTR_TAC asm  ORELSE  ACCEPT_TAC asm)
}
\noindent searches the assumptions for either a contradiction or the desired
conclusion. The tactic
{
   FIRST_ASSUM MATCH_MP_TAC
}
\noindent searches the assumption list for an implication whose conclusion
matches the goal, reducing the goal to the antecedent of the corresponding
instance of this implication.

\SEEALSO
ASSUM_LIST, EVERY, EVERY_ASSUM, FIRST, FIRST_X_ASSUM, MAP_EVERY, MAP_FIRST.

\ENDDOC