# Tools Options

The Tools options panel controls how Regina works with third-party software.

The settings here are:

Diagnostic messages from SnapPea

  Specifies whether the SnapPea kernel should write diagnostic messages to the terminal.

  When you are working with the SnapPea kernel (for instance, if you are using a SnapPea triangulation, or visiting Regina's SnapPea tab), the SnapPea kernel sometimes sends out messages indicating what it is doing. An example of such a message might be “Computing hyperbolic structure . . .”.

  If this option is checked, then all such messages will be written to the terminal from which you started Regina. If this is unchecked (or if you started Regina some other way, such as from a menu or taskbar), then these messages will be suppressed.

Use default PDF viewer

  If checked, Regina will open PDF packets using the default PDF viewer on your computer (for instance, this might be Evince under GNOME, or Preview under MacOS). If unchecked, Regina will use the custom PDF viewer specified in the text box below.

Custom PDF viewer

  If you have unchecked Use default PDF viewer (as described above), here you can specify the command to start your preferred PDF viewer (such as `xpdf` under GNU/Linux, or `open` under MacOS). Regina will look for this command on the default search path. If your viewer is installed somewhere unusual then you will need to provide the full path to the executable (such as `/usr/local/bin/xpdf`).

  You may include additional command-line arguments here (so, for instance, MacOS users might enter `/usr/bin/open -a Preview`). Regina will automatically add the location of the PDF document to the end of this command, and the entire command will be passed to a shell for execution.

GAP executable

  Tells Regina where to find GAP (Groups, Algorithms and Programming). GAP is not required by Regina, but if it is installed then it can help simplify group presentations.

  This setting should be the name of the command that starts GAP (the default is simply `gap`). Regina will look for this command on the default search path. If you have installed GAP somewhere unusual then you will need to provide the full path to the executable (such as `/usr/local/bin/gap`).