Two classes of graph-based crossover are described in : multipoint crossover starts from a cut that is chosen to minimize topological disruption and a reconnection procedure that ensures connectedness of the children . Subgraph crossover, in contrast, identifies a subgraph in each parent and then proceeds by reconnecting them. In MEGA , crossover is guided by retrosynthetic information obtained from RECAP or affects single bonds or rings , see also . The graph-based GA described in uses reaction SMILES to implement its crossover operator. EvoMD , finally, is defined on the binary adjacency matrices of the parent graphs. Even though graph-based GAs are not at all uncommon, very little is known about the mathematical properties of these crossover operators.