1. A computer program product comprising one or more computer-readable media having thereon computer-executable instructions that, when executed by one or more processors of a computing system, cause the computing system to perform the following: an act of accessing a data structure that represents a symbolic expression; an act of accessing a representation of a match that represents a mathematical identity; an act of determining that the match has an associative commutative operator, and that each variable in the match is used only once in the match, except for just one reaction variable that has a plurality of instances in the match and which includes at least one instance that is not a direct argument of an associative commutative operator; an act of inverting the match around the reaction variable that has a plurality of instances in the match in response to the act of determining; and an act of applying the inverted match to the symbolic expression to thereby transform the symbolic expression.