For all maps from synthon substructures to synthon sets that are compatible with O2.9 and O4.9, try to match synthon substructures in the mapped synthon sets ) This shows an example for a valid decomposition, together with the total number of unlabeled decompositions that arise for this structure. (2.) The subgraphs used for the connector region heuristic are highlighted, for the two decompositions that result in hits, and for one out of the 409 eliminated decompositions. The heuristic eliminates over 99% of the unlabeled decompositions. (3.) For the remaining unlabeled decompositions, all labeled decompositions are enumerated. In this example we assume that we consider synthon reactions with up to 3 different connector vertex types, therefore we get 1 3 (1!) = 3 labeled decomp. for the single split decomposition, and 2 3 (2!) = 6 labeled decomp. for the double split case. (4.) The most complicated fragment (measured by number of set fragment fingerprint bits) is considered first for actual substructure search in the synthon sets (5.) Finally, matching synthons are searched according to the maps that are compatible with all heuristics. types. Narrowing query features include the possibility to prohibit further substitution on atoms or to require atoms of the query substructure to have a specific number of (unspecified) neighbor atoms.