About Working with Variables in Symbolic Expressions
Use the following keywords to perform operations on variables in a symbolic expression:
• substitute—Replaces all occurrences of a variable in an expression with a number, another variable, or an expression.
• assume—Makes assumptions about the domain of a variable, for example, that the variable is an integer or a real number.
• explicit—Clears a previous definition of a variable, so that you can use it as a free variable.