[cells-devel] *causation*

[Kenny Tilton]

It's back. *causation* is now bound to a "stack" of propagating cells, 
where the last element of the list is the original cause.

Of course, to achieve proper backout this really needs to become more 
history than stack, because propagation sweeps a tree of dependencies, 
and the FAIL even can arise in a second branch of propagation, at which 
point a stack will have lost track of the first branch of propagation.

Over to you, Prolog fans.

kenny