I want to define a coordinate ring of P1*P1*P3, i.e. K[u1,u2,v1,v2,w1,w2,w3,w4] .Here u1,u2 has grade (1,0,0). v1,v2 has grade (0,1,0). w1,w2,w3,w4 has grade (0,0,1). As for the ordering, I have no specific choice, maybe just the naive choice u1<u2, v1<v2,w1<w2<w3<w4,(1,0,0)<(0,1,0)<(0,0,1).