Atom mapping, which relies on rearrangement of atoms in chemical transformations, is promising to tackle this problem. Atom mapping describes the exact transformation and reveals the missing species on the product side. Jaworski et al. utilised graph-theoretical considerations and chose 20 chemical rules / heuristics to correct mapping of reactions. This method attempts to complete stoichiometry firstly by adding small molecules such as acetaldehyde, ammonia, and others to balance the reactions and, secondly, by fitting reactions into popular reaction templates and adding the missing parts. Only if such attempts fail, atom mapping is employed.