Future move proposal engines could be made more efficient by taking advantage of basic chemical information. For example, if a double bond was already specified between a carbon and another atom, that carbon atom cannot have four bonds; however, as currently implemented, SMIRKY will occasionally propose moves which attempt to add a "X4" decorator to that carbon. We could take this concept one step further by learning which decorators can productively be applied to which atoms. For example, hydrogen can only have one bond and it is always single, so adding decorators to a hydrogen atom or its connecting bond will never usefully impact the separation of fragment types. Currently, SMIRKY makes many naïve moves, wasting many of its iterations generating SMIRKS patterns that cannot help separate fragments for these and other reasons.