Parameters | Utilities | Fixed Effects for Differential Expression

To specify interactions between effect, type an asterisk (*) between the effects. For example, assuming A and B are listed as Categorical Variables, typing A B A*B specifies variables A and B, and the interaction between A and B, as effects.

A vertical bar (|) can be used to create main effects and interactions. For example, typing A|B is the same as typing A B A*B.