gap> mat := [[1,0,0],[0,0,2],[0,2,0]]*Z(5)^0; [ [ Z(5)^0, 0*Z(5), 0*Z(5) ], [ 0*Z(5), 0*Z(5), Z(5) ], [ 0*Z(5), Z(5), 0*Z(5) ] ] gap> phi := PolarityOfProjectiveSpace(mat,GF(25)); <polarity of PG(2, GF(5^2)), > gap> BaseField(phi); GF(5^2)