OESystem::OEIterBase<OEAtomBase> *
         OEAcyclicPath(const OEAtomBase *bgn, const OEAtomBase *end)

Returns an iterator over the atoms in order connecting bgn to end through the molecular graph without traversing rings. Both bgn and end will be returned in the iterator. Therefore, bgn will always be the first atom in the iterator and end will always be the last atom in the iterator if a acyclic path through the molecule exists. If no path exists, only bgn will be returned in the iterator.