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, function, expression, or number with another variable, function, expression, or number.
• 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.