GAP Manual: 3.11. Help Index

??topic

?? looks up topic in GAP's index and prints all the index entries that contain the substring topic. Then you can decide which section is the one you are actually interested in and request this one.

    gap> ??help
        help ______________________________________________________ Index
        Help
        Reading Sections (help!scrolling)
        Format of the Sections (help!format)
        Browsing through the Sections (help!browsing)
        Redisplaying a Section (help!redisplaying)
        Abbreviating Section Names (help!abbreviating)
        Help Index
    gap> 

The first thing on each line is the name of the section. If the name of the section matches topic nothing more is printed. Otherwise the index entry that matched topic is printed in parentheses following the section name. For each section only the first matching index entry is printed. The order of the sections corresponds to their order in the GAP manual, so that related sections should be adjacent.