applications.collages.gridAlgebra:
( 4,
  {
    F0 = 5bc-6cd-9ab-10da,
    F = 0ab-4bc-6da-7ab-8ab-9da-11bc-15ab,
    G = 3ab-0ab-4bc-6da-7ab-8ab-9da-11bc-15ab,
    S0 += { },
    S1 += { filledPolygon((-20,-20),(20,-20),(20,20))[1,1,1] },
    S += { filledCurve((20,-20),(-20,-20),(20,20))[.5,.5,.5] }
  }
)
