def has_rewrite(th, t, *, sym=False, conds=None):
"""Returns whether a rewrite is possible on a subterm of t.
This can serve as a pre-check for top_sweep_conv, top_conv, and
bottom_conv applied to rewr_conv.
th -- either the name of a theorem, or the theorem itself.
t -- target of rewriting.
conds -- optional list of theorems matching assumptions of th.
"""
if isinstance(th, str):
th = theory.get_theorem(th)
if sym:
th = Thm.symmetric(th)
As, C = th.prop.strip_implies()
if conds is None:
conds = []
if not C.is_equals() or len(As) != len(conds):
return False
if set(term.get_svars(As + [C.lhs])) != set(term.get_svars(As + [C])):
return False
ts = [cond.prop for cond in conds]
inst = Inst()
try:
inst = matcher.first_order_match_list(As, ts, inst)
except matcher.MatchException:
return False
def rec(t):
if not t.is_open() and matcher.can_first_order_match(C.lhs, t, inst):
return True
if t.is_comb():
return rec(t.fun) or rec(t.arg)
elif t.is_abs():
_, body = t.dest_abs()
return rec(body)
else:
return False
return rec(t)
def testSymmetric(self):
th = Thm([A], Term.mk_equals(x, y))
self.assertEqual(Thm.symmetric(th), Thm([A], Term.mk_equals(y, x)))
def testSymmetric(self):
th = Thm([A], Eq(x,y))
self.assertEqual(Thm.symmetric(th), Thm([A], Eq(y,x)))