gap&gt; pg := PG(3,5);
ProjectiveSpace(3, 5)
gap&gt; p := Random(Points(pg));
&lt;a point in ProjectiveSpace(3, 5)&gt;
gap&gt; l := Random(Lines(p));
&lt;a line in ProjectiveSpace(3, 5)&gt;
gap&gt; plane := Random(Planes(l));
&lt;a plane in ProjectiveSpace(3, 5)&gt;
gap&gt; flag := FlagOfIncidenceStructure(pg,[l,plane]);
&lt;a flag of ProjectiveSpace(3, 5)&gt;
gap&gt; IsIncident(flag,l);
true
gap&gt; IsIncident(l,flag);
true
