# Commands Overview

Commands are used both to construct and manipulate expressions. Typically, single-character keystrokes are used to invoke commands. For example, the "s" keystroke normally runs the Simplify command on the highlighted expression.

The commands described in this section are the most commonly used commands. The list of commands available when a document is loaded into the application depend on which libraries are included in the document. You can see the list of libraries in the Document Explorer. See Libraries and References for more information.

Commands can act in several different ways. The simplest case is when a command only modifies the highlighted expression. Some commands modify the entire expression even when only part of the expression is highlighted. An example is the Move command. If the expression is:

x - 1 = 0

and the "1" is highlighted, the Move command will change the expression to:

x = 1

Here the entire expression has been altered, not just the highlighted term. Whether a command acts only on the highlighted expression or on the whole expression depends on type definition of the function assigned to the command. See Functions Executed by Commands for more information.

The All command provides a way to see the commands that are available. Most of the commands can be seen in here. You can apply the All command by pressing the "a" key. You can execute the commands shown in the pop-up when the All command is applied by selecting any of the commands shown in the pop-up. The list of commands shown in the pop-up can depend on the expression that is currently highlighted. The commands included can be modified and extended if desired.

The commands available in a document depend on the libraries that are loaded. New commands can be created both within the current document and in libraries loaded in the current document. For more information see Creating and Editing Commands

Note that most of the commonly used commands have keystrokes that fall on the left half of the keyboard. To some extent this is coincidence, but we have tried to keep the commands on the left half of the keyboard as much as possible because it allows executing commands with the left hand and moving the highlight with the right hand on the arrow keys. This makes it possible to rapidly execute multiple commands on different terms in an expression without having to switch back and forth between mouse and keyboard.