applications.collages.collageAlgebra:
  {
    chair = { polygon((0,0),(1,0),(1,1),(.5,1),(.5,.5),(0,.5)) },
    blackChair = { filledPolygon((0,0),(1,0),(1,1),(.5,1),(.5,.5),(0,.5))<1,1,0> },
            
    invert = similarity((0,.5) -> (0,0), (0,0) -> (1,0)),
    invert = <invert>,
    
    r1 = scale(.5) . translate(.5,0),
    r2 = scale(.5) . translate(.25,.25),
    r3 = scale(.5) . rotate(-90) . translate(0,.5),
    r4 = scale(.5) . rotate(90) . translate(1,.5),
    refine = <r1,r2,r3,r4>,
    
    lighten = colourOperation(r|.2:0, g|.3:0, b|.2:1)
  }
