PAT_CONV : term -> conv -> conv

SYNOPSIS
Apply a conversion at subterms identified by a ``pattern'' lambda-abstraction.

DESCRIPTION
The call PAT_CONV `\x1 ... xn. t[x1,...,xn]` cnv gives a new conversion that applies cnv to subterms of the target term corresponding to the free instances of any xi in the pattern t[x1,...,xn]. The fact that the pattern is a function has no logical significance; it is just used as a convenient format for the pattern.

FAILURE CONDITIONS
Never fails until applied to a term, but then it may fail if the core conversion does on the chosen subterms.

EXAMPLE
Here we choose to evaluate just two subterms:
  # PAT_CONV `\x. x + a + x` NUM_ADD_CONV `(1 + 2) + (3 + 4) + (5 + 6)`;;
  val it : thm = |- (1 + 2) + (3 + 4) + 5 + 6 = 3 + (3 + 4) + 11
while here we swap two particular quantifiers in a long chain:
  #  PAT_CONV `\x. !x1 x2 x3 x4 x5. x` (REWR_CONV SWAP_FORALL_THM)
      `!a b c d e f g h. something`;;
  Warning: inventing type variables
  Warning: inventing type variables
  val it : thm =
    |- (!a b c d e f g h. something) <=> (!a b c d e g f h. something)

SEE ALSO
ABS_CONV, BINDER_CONV, BINOP_CONV, PATH_CONV, RAND_CONV, RATOR_CONV.