In this case, a compressed SMIRKS retains decorators on atoms, but they are arranged differently. The atoms store all combinations of decorators, however it is also useful to know which decorators are always included on an atom. In the compressed SMIRKS, decorators, which atoms from all molecules have in common, are and'd (;) to the end of that SMIRKS. Consider again atom 2 in the ethanol/propene example. Atom 2 occurs in two different environments, but these two cases share some decorators. In the complex SMIRKS ("[#6H2X4x0!r+0A,#6H1X3x0!r+0A:2]") all decorators are treated separately, but in the compressed SMIRKS ("[#6H2X4,#6H1X3 ;!r;+0;x0;A:2]") the common decorators are and'd to the end. This is useful when trying to isolate which decorators are important for telling one cluster apart from another.