-- -*- M2-comint -*- hash: 15888710335351403701

i1 : Phi = rationalMap({veronese(1,4,ZZ/33331)},Dominant=>true);

o1 : MultirationalMap (dominant rational map from PP^1 to curve in PP^4)

i2 : Psi = last graph rationalMap PP_(ZZ/33331)^(1,3);

o2 : MultirationalMap (rational map from threefold in PP^3 x PP^2 to PP^2)

i3 : (X,Y,Z,W) = (source Phi,target Phi,source Psi,target Psi);

i4 : Eta = Phi || Psi;

o4 : MultirationalMap (rational map from X x Z to Y x W)

i5 : Psi || Eta;

o5 : MultirationalMap (rational map from Z x X x Z to W x Y x W)

i6 : Psi || Eta || Phi;

o6 : MultirationalMap (rational map from Z x X x Z x X to W x Y x W x Y)

i7 : assert(oo == (Psi || Eta) || Phi and (Psi || Eta) || Phi == Psi || (Eta || Phi))

i8 : 
