Comment #11 on issue 1309 by akshaysrinivasan: implement backward chaining
for rules
http://code.google.com/p/sympy/issues/detail?id=1309
I was thinking of maybe storing implications as Boolean expressions which
are always
true.
>>> i=Bool('Integer')
>>> o=Bool('Odd')
>>> e=Bool('Even')
>>> z=Bool('Zero')
>>> e=(o | e | z)
>>> (e & i) | (~e & ~i) ##Double implication e <-> i
(~Integer & ~(Odd | Zero | Even)) | ((Odd | Zero | Even) & Integer)
>>> expr=(e & i) | (~e & ~i)
>>> expr
(~Integer & ~(Odd | Zero | Even)) | ((Odd | Zero | Even) & Integer)
>>> expr.eval(Odd=True)
Integer
>>> ~o | i ##Implication o -> i
~Odd | Integer
>>> (~o | i).eval(Odd=True)
Integer
>>> (~o | i).eval(Integer=True)
1
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