The simplify command is used to apply simplification rules to an expression.

The Error, (in simplify/do) invalid simplification command message occurs when parameters passed to do not comply with a valid calling sequence.

Example 1

In this instance, the parameters do not match any of the valid calling sequences of .

Solution 1:

Enclose the equation x=y in a set.

Solution 2:

For a direct substitution, you can also use the eval command.

Example 2

Here,  provides a side relation that should be used when simplifying the expression . The side relations passed to  must be a set or list of equations. For more information on side relations, see simplify/siderels.

Solution:
Enclose the equation in a set.

eval, simplify,  simplify/siderels