applications.collages.gridAlgebra:
( 2,
  {
    F = 0ab-1bc-2dc-3ab,
    G = 0ab-1ab-2ab-3ab,
    S += { filledPolygon((0,18),(0,0),(18,0),(18,-18),(-18,-18),(-18,18))[.4,.4,.4] },
    A += { filledPolygon((0,18),(0,0),(18,0),(18,-18),(-18,-18),(-18,18))[.6,.6,.6] },
    B += { filledPolygon((0,0),(18,0),(18,18),(0,18))[1,1,1] }
  }
)
