i1 :  A GM fourfold of discriminant 20
X = specialGushelMukaiFourfold("17",ZZ/33331);
o1 : ProjectiveVariety, GM fourfold containing a surface of degree 9 and sectional genus 2

i2 : describe X
o2 = Special GushelMukai fourfold of discriminant 20
containing a surface in PP^8 of degree 9 and sectional genus 2
cut out by 19 hypersurfaces of degree 2
and with class in G(1,4) given by 6*s_(3,1)+3*s_(2,2)
Type: ordinary
(case 17 of Table 1 in arXiv:2002.07026)

i3 : time f = detectCongruence(X,Verbose=>true);
 used 23.3384s (cpu); 9.40395s (thread); 0s (gc)
number lines contained in the image of the quadratic map and passing through a general point: 7
number 1secant lines = 6
number 3secant conics = 1
o3 : Congruence of 3secant conics to surface in a fivefold in PP^8

i4 : Y = ambientFivefold X;  del Pezzo fivefold containing X
o4 : ProjectiveVariety, 5dimensional subvariety of PP^8

i5 : p := point Y  random point on Y
o5 = point of coordinates [7214, 1460, 7057, 2440, 15907, 14345, 5937, 13402, 1]
o5 : ProjectiveVariety, a point in PP^8

i6 : time C = f p;  3secant conic to the surface
 used 0.6415s (cpu); 0.397615s (thread); 0s (gc)
o6 : ProjectiveVariety, curve in PP^8 (subvariety of codimension 4 in Y)

i7 : S = surface X;
o7 : ProjectiveVariety, surface in PP^8 (subvariety of codimension 3 in Y)

i8 : assert(dim C == 1 and degree C == 2 and dim(C*S) == 0 and degree(C*S) == 3 and isSubset(p,C) and isSubset(C,Y))
