gap&gt; ps := PG(3,7);
ProjectiveSpace(3, 7)
gap&gt; point := VectorSpaceToElement(ps,[1,2,0,0]*Z(7)^0);
&lt;a point in ProjectiveSpace(3, 7)&gt;
gap&gt; plane := VectorSpaceToElement(ps,[[1,0,0,0],[0,1,0,0],[0,0,0,1]]*Z(7)^0);
&lt;a plane in ProjectiveSpace(3, 7)&gt;
gap&gt; flag := FlagOfIncidenceStructure(ps,[point,plane]);
&lt;a flag of ProjectiveSpace(3, 7)&gt;
gap&gt; lines := ShadowOfFlag(ps,flag,"lines");
&lt;shadow lines in ProjectiveSpace(3, 7)&gt;
