// The matrix generators of BI120 from 7.8 K5 := CyclotomicField(5); GL2 := GL(2, K5); x := ep + ep^-1; // x is 2*cos 2*pi/5 approx eq 0.618034 r5 := 2*x+1; r5^2; x eq (-1+r5)/2; Z := elt< GL2 | -ep^3,0,0,-ep^2 >; X := elt< GL2 | (-ep+ep^4)/r5, (ep^2-ep^3)/r5, (ep^2-ep^3)/r5, (ep-ep^4)/r5 >; X^2; (X*Z)^3; BI120 := sub< GL2 | [X, Z] >; Order(BI120); IsIsomorphic( quo< BI120 | X^2 >, Alt(5));