i1 : Phi = rationalMap({veronese(1,4,ZZ/33331)},Dominant=>true);
o1 : MultirationalMap (dominant rational map from PP^1 to curve in PP^4)
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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)
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i3 : (X,Y,Z,W) = (source Phi,target Phi,source Psi,target Psi);
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i4 : Eta = Phi || Psi;
o4 : MultirationalMap (rational map from X x Z to Y x W)
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i5 : Psi || Eta;
o5 : MultirationalMap (rational map from Z x X x Z to W x Y x W)
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i6 : Psi || Eta || Phi;
o6 : MultirationalMap (rational map from Z x X x Z x X to W x Y x W x Y)
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i7 : assert(oo == (Psi || Eta) || Phi and (Psi || Eta) || Phi == Psi || (Eta || Phi))
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