TeX/let

Description
allows you to copy the content of a command into a new command.

Unlike making a macro that calls the original command,  allows you to subsequently modify the old command while still retaining its functionality under the new command. It is often used to change the behaviour of an existing command (but not replace it entirely). In such cases  may fail, and   may be required.

The equal sign (and the spaces before it) are not required, but may be useful in some special cases where the second argument is a space or a equal sign.

Examples
If one wanted to change the behaviour of a command  wherever it was called, such that   were executed first, the following may seem appropriate. This, however, will create a recursive loop where calling  will repeatedly call itself until the computer's memory is exhausted.

In order to change the behaviour of  to include some other behaviour, the   command is used: The first line copies the contents of the  command into the new command. The second line modifies the  command to execute   followed by the original contents of the   command (which are now stored in  ).