applications.collages.collageAlgebra:
{
  ntColour = const(.8),

  line = { filledPolygon((-1,0),(0,1),(1,0),(0,-1))<.5,.5,.5> },
  
  f1 = rotate(180) . similarity((-1,0) -> (-1,0), (1,0) -> (0,-1)),
  f2 = rotate(180) . similarity((-1,0) -> (1,0), (1,0) -> (0,-1)),
  F = <f1, f2>,
  
  col1 = colourOperation(r||.2:0, g|.2:0, b||.2:0),
  col2 = colourOperation(r|.2:1, g||.2:0, b| .2:0)
}