ddc-core-flow: rate inference: found an error in the paper! the 'sole parents' lemma is actually incorrect if one node is the child of another. so 'parents(a,b)' may have multiple possibilities if 'a' is parent of 'b'. in this case, we need to use the most specific parents, which would be '(a,a)'.
ddc-core-flow: 1. simplify integer program before passing to cbc. 2. fusion preventing path must check for paths in either direction. 3. when adding filter constraints, check if there is a fusion preventing path between any of the parents; if there is, they cannot be fused.