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\DOC ASSUME_TAC
\TYPE {ASSUME_TAC : thm_tactic}
\SYNOPSIS
Adds an assumption to a goal.
\KEYWORDS
tactic, assumption.
\DESCRIBE
Given a theorem {th} of the form {A' |- u}, and a goal, {ASSUME_TAC th}
adds {u} to the assumptions of the goal.
{
A ?- t
============== ASSUME_TAC (A' |- u)
A u {{u}} ?- t
}
\noindent Note that unless {A'} is a subset of {A}, this tactic is invalid. The
new assumption is unlabelled; for a named assumption use {LABEL_TAC}.
\FAILURE
Never fails.
\EXAMPLE
One can add an external theorem as an assumption if desired, for example so
that {ASM_REWRITE_TAC[]} will automatically apply it. But usually the theorem
is derived from some theorem-tactical, e.g. by discharging the antecedent of an
implication or doing forward inference on another assumption. For example iff
faced with the goal:
{
# g `0 = x ==> f(2 * x) = f(x * f(x))`;;
}
\noindent one might not want to just do {DISCH_TAC} or {STRIP_TAC} because the
assumption will be {`0 = x`}. One can swap it first then put it on the
assumptions by:
{
# e(DISCH_THEN(ASSUME_TAC o SYM));;
val it : goalstack = 1 subgoal (1 total)
0 [`x = 0`]
`f (2 * x) = f (x * f x)`
}
\noindent after which the goal can very easily be solved:
{
# e(ASM_REWRITE_TAC[MULT_CLAUSES]);;
val it : goalstack = No subgoals
}
\USES
Useful as a parameter to various theorem-tacticals such as {X_CHOOSE_THEN},
{DISCH_THEN} etc. when it is simply desired to add the theorem that has been
deduced to the assumptions rather than used further at once.
\SEEALSO
ACCEPT_TAC, DESTRUCT_TAC, LABEL_TAC, STRIP_ASSUME_TAC.
\ENDDOC
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