gap&gt; ps := PG(3,13);
ProjectiveSpace(3, 13)
gap&gt; plane := Random(Planes(ps));
&lt;a plane in ProjectiveSpace(3, 13)&gt;
gap&gt; line := Random(Lines(plane));
&lt;a line in ProjectiveSpace(3, 13)&gt;
gap&gt; point := Random(Points(line));
&lt;a point in ProjectiveSpace(3, 13)&gt;
gap&gt; flag := FlagOfIncidenceStructure(ps,[point,line,plane]);
&lt;a flag of ProjectiveSpace(3, 13)&gt;
gap&gt; IsChamberOfIncidenceStructure(flag);
true
