Status: Accepted
Owner: ----
Labels: Type-Enhancement Priority-Critical Milestone-Release0.6.5

New issue 1309 by fabian.seoane: implement backward chaining for rules
http://code.google.com/p/sympy/issues/detail?id=1309

Currently, our core.facts module only supports forward-chaining.
Bakcward-chaining support was planned but never completed.

(definition: Backward chaining starts with a list of goals (or a
hypothesis) and works backwards from the consequent to the antecedent to
see if there is data available that will support any of these consequents)

For the new assumption system, this will mean that query(x, 'integer',
Assume(x, 'odd')) will return True without the need to write any code since
odd ==> integer.

This issue should implement backward-chaining, either in this module or in
a separate one.

related resources are:
    - http://en.wikipedia.org/wiki/Backward_chaining

    - aima-python: http://code.google.com/p/aima-python/ . They have
implemented a nice logic module which supports backward-chaining. However,
I could not get it to work beyond the examples they provide.

    - PyKE: http://pyke.sourceforge.net/about_pyke/index.html

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