For each group library there is an extraction function. This function allows you to extract single groups from the library.
The name of the extraction function always ends with Group and begins
with a name that hints at the nature of the library. For example the
The Primitive Groups Library) is called PrimitiveGroup, and the extraction
The 2-Groups Library) is called TwoGroup.
What arguments the extraction function accepts, and how they are interpreted is described in the sections that describe the individual group libraries.
For example
PrimitiveGroup( 10, 4 );
returns the 4-th primitive group of degree 10.
The reason for the extraction function is as follows. A group library is usually not stored as a list of groups. Instead a more compact representation for the groups is used. For example the groups in the library of 2-groups are represented by 4 integers. The extraction function hides this representation from you, and allows you to access the group library as if it was a table of groups (two dimensional in the above example).
GAP 3.4.4