applications.collages.gridAlgebra:
( 2,
  {
    F = 0ab-1ba-2dc-3cd,
    G = 0ab-1ab-2ab-3bc,
    E += { filledPolygon((-20,14),(20,14),(20,18),(-20,18))[.6,.6,.6],
           filledPolygon((-20,-14),(20,-14),(20,-18),(-20,-18))[.6,.6,.6] },
    C += { filledPolygon((-20,14),(-14,14),(-14,20),(-18,20),(-18,18),(-20,18))[.6,.6,.6],
           filledPolygon((-20,-14),(14,-14),(14,20),(18,20),(18,-18),(-20,-18))[.6,.6,.6] },
    H = 0ab-1ab-2ab-3ab
  }
)
