i1 : S = PP_(ZZ/65521)[2,2];
o1 : ProjectiveVariety, surface in PP^5
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i2 : Y = ambient S;
o2 : ProjectiveVariety, PP^5
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i3 : X = specialCubicFourfold S;
o3 : ProjectiveVariety, cubic fourfold containing a surface of degree 4 and sectional genus 0
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i4 : f = detectCongruence(X,1);
o4 : Congruence of 2-secant lines to S in Y
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i5 : F = map f;
o5 : MultirationalMap (dominant rational map from Y to hypersurface in PP^5)
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i6 : Q = target F
o6 = Q
o6 : ProjectiveVariety, hypersurface in PP^5
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i7 : f;
o7 : Congruence of 2-secant lines to S in Y; parameter space: Q
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i8 : p = point Y;
o8 : ProjectiveVariety, a point in PP^5
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i9 : assert(f p == F^* F p)
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