SubstituteSingleReplace[expr, aListOfRules, (optional On)]

Aliases: SubSingleRep

Description: Replaces one symbol or sub-expression in the expression by another expression as specified by the rule. (See Wolfram's Mathematica 2.* page 54.)

Arguments: $expr$ is an algebraic expression. $aListOfRules$ is a single rule or list of rules specifying the substitution to be made. On = save rules to Rules.temp, temporarily over-rides SaveRules[Off]. `Off' can not over-ride SaveRules[On].

Comments / Limitations: The symbols /. and //. are often used in Mathematica as methods for substituting one expression for another. This method of substitution often does not work when the expression to be substituted is a subexpression within a (noncommutative) product. This Substitute command is the noncommutative analogue to /.