isMorphism -- whether a rational map is a morphism

i1 : phi = quadroQuadricCremonaTransformation(5,1)

o1 = -- rational map --
     source: Proj(QQ[x, y, z, t, u, v])
     target: Proj(QQ[x, y, z, t, u, v])
     defining forms: {
                             2
                      y*z - v ,
                      
                             2
                      x*z - u ,
                      
                             2
                      x*y - t ,
                      
                      - z*t + u*v,
                      
                      - y*u + t*v,
                      
                      t*u - x*v
                     }

o1 : RationalMap (Cremona transformation of PP^5 of type (2,2))

i2 : isMorphism phi

o2 = false

i3 : phi' = last graph phi;

o3 : MultihomogeneousRationalMap (birational map from 5-dimensional subvariety of PP^5 x PP^5 to PP^5)

i4 : isMorphism phi'

o4 = true