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### B.3. TeX and LaTeX commands for tracing

In this section we discuss tools and techniques for tracing and for displaying status information—for example, finding out why something is strangely spaced on the page or why your own command definition does the wrong thing.

#### B.3.1. Displaying command definitions and register values

In many situations it is useful to get some information about LaTeX’s current internals, the precise definitions of commands, the values of registers, and so on. For example, if the use of \newcommand reports that the command to be defined is already defined, you may want to know its current definition, to ensure that you do not redefine an important command.

Displaying command definitions

For this purpose TeX offers the command \show, which displays the definition of the token following it and then stops and displays a question mark while waiting for user intervention. For example, after defining \xvec as in Example A-1-4 on page 844, we can display its definition as follows:

PREVIEW

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