applications.collages.gridAlgebra:
( 2,
  {
    F = 0ab-1ba-2ab-3ba,
    G = 0da-2cd-3cb,
    H = 1ab-3ab,
    S0 += {},
    S  += { filledPolygon((-18,-18),(18,18),(18,-18))[.5,.5,.5] },
    A  += { filledPolygon((-18,-18),(18,-18),(-18,18))[1,1,1] }
  }
)
