applications.collages.collageAlgebra("algebra for P. trees"):
{
  ntColour = const(.8),

  tipX = %const(.5),
         const(.32898993),
  tipY = %const(1 + .5),
         const(1 + .46984631),

  part = { filledPolygon((0,0),(1,0),(1,1),(#tipX, #tipY),(0,1)) },
  sample-outline = { polygon((0,0),(1,0),(1,1),(#tipX, #tipY),(0,1))},
  sample-filled = { filledPolygon((0,0),(1,0),(1,1),(#tipX, #tipY),(0,1))[#ntColour,#ntColour,#ntColour] }
                       + #sample-outline,
  sample-arrow = { filledPolygon((0,0),(.05,.2),(-.05,.2))},
  sample = #sample-filled + #sample-outline + #sample-arrow,
  S = #sample,
  
  f1 = similarity((0,0) -> (0,1), (1,0) -> (#tipX, #tipY)),
  f2 = similarity((0,0) -> (#tipX, #tipY), (1,0) -> (1,1)),
  F = < #part, f1, f2 >,
  
  flip = scale(-1,1) . translate(1,0),
  flip = <flip>
  
  
}
