applications.collages.gridAlgebra:
( 2,
  {
    F = 0ab-1da-2ab-3ab,
    G = 1ab-2ab,
    H = 0ab-1ab-2da,
    I = 1bc-2cd-3ab,
    J = 0ba-1ab,
    S += {},
    M += { filledPolygon((-20,20),(-20,19),(19,-20),(20,-20),(20,-19),(-19,20)) },
    O += { filledPolygon((-20,-20),(-20,-18.6),(20,-18.6),(20,-20)) }
  }
)
