1.4.2 Fast Actions

The fast-action bar contains user-interface controls that are used frequently. These controls are designed to be generic. That is, they adapt to a wide range of expressions and apply transformations appropriate to the kind of expression at hand. Fast-action transformations are explained in great detail starting with §3.2.1. In preview, here are summaries of actions initiated from the fast-action bar.

• Straight left and right arrows ( and ) perform commutative and other rearrangements. See §3.2.1.
• Hooked left and right arrows ( and ) perform undo and redo actions. See §8.1.5
• Simplify combines constants and reduces the operator count. See §3.2.2.
• Distribute expands expressions and increases the operator count. See §3.2.3
• Factor recognizes and combines common subexpressions. See §3.2.4.
• Evaluate binds variables and applies complex arithmetic reductions. See §3.2.5.

The left and right hooked arrows perform undo and redo actions. As an expression is manipulated, the actions can be replayed by moving backwards and forwards through the undo list. However, as soon as an action is applied that changes the displayed expression, the redo portion of the list is truncated. Undo and Redo are sensitive to long touches. When long touches are used, Undo moves to the very first element of the list and Redo moves to the very last one.