If a subexpression is selected in the expression editor, then any menu command will be applied to that subexpression.
For example, enter the expression (x+1)*(x+2)*(x-1) in the expression editor. Note that use the abilities of the editor to make this easier. First, enter x+1. Select this with the up arrow, then type * followed by x+2. Select the x+2 with the up arrow and then type * followed by x-1. Using the up arrow again will select the x-1. Select the entire expression with the up arrow, and then select eval from the M menu. This will put all factors at the same level. Suppose you want the factors (x+1)*(x+2) to be expanded. You could select (x+1)*(x+2) with the mouse and do one of the following:
There are also keystroke commands that use to operate on subexpressions that you have selected. There are the usual Ctrl+Z and Ctrl+Y for undoing and redoing. Some of the others are given in Table 2.1.