## Using Ordinary TeX Commands

Inside a region delineated by @iftex and @end iftex, you can embed some PlainTeX commands. Info will ignore these commands since they are only in that part of the file which is seen by TeX. You can write the TeX commands as you would write them in a normal TeX file, except that you must replace the \' used by TeX with an @'. For example, in the @titlepage section of a Texinfo file, you can use the TeX command @vskip to format the copyright page. (The @titlepage command causes Info to ignore the region automatically, as it does with the @iftex command.)

However, many features of PlainTeX will not work, as they are overridden by features of Texinfo.

You can enter PlainTeX completely, and use \' in the TeX commands, by delineating a region with the @tex and @end tex commands. (The @tex command also causes Info to ignore the region, like the @iftex command.)

For example, here is a mathematical expression written in PlainTeX:

@tex
$$\chi^2 = \sum_{i=1}^N \left (y_i - (a + b x_i) \over \sigma_i\right)^2$$
@end tex
`

The output of this example will appear only in a printed manual. If you are reading this in Info, you will not see anything after this paragraph. In a printed manual, the above expression looks like this: