Nice equations for nice groups

Nice trinomial equations are given for unramified coverings of the affine line in nonzero characteristicp with PSL(m,q) and SL(m,q) as Galois groups. Likewise, nice trinomial equations are given for unramified coverings of the (once) punctured affine line in nonzero characteristic p with PGL(m,q) and GL(m,q) as Galois groups. Here m>1 is any integer and q>1 is any power of p