grassmannianHull -- grassmannian hull of a Gushel-Mukai fourfold

i1 : X = specialGushelMukaiFourfold("21",ZZ/33331);

o1 : ProjectiveVariety, GM fourfold containing a surface of degree 12 and sectional genus 5

i2 : describe X

o2 = Special Gushel-Mukai fourfold of discriminant 26(')
     containing a surface in PP^8 of degree 12 and sectional genus 5
     cut out by 16 hypersurfaces of degree 2
     and with class in G(1,4) given by 7*s_(3,1)+5*s_(2,2)
     Type: ordinary
     (case 21 of Table 1 in arXiv:2002.07026)

i3 : Y = grassmannianHull X;

o3 : ProjectiveVariety, 5-dimensional subvariety of PP^8

i4 : isSubset(X,Y)

o4 = true

i5 : Y!
dim:.................. 5
codim:................ 3
degree:............... 5
sectional genus:...... 1
generators:........... 2^5 
linear normality:..... true
connected components:. 1
purity:............... true
dim sing. l.:......... -1