map.rb

class Fork < Map
  def balance(* in [RedFork[a, xk, xv, b], yk, yv, RedFork[c, zk, zv, d]]) =
    RedFork[BlackFork[a, xk, xv, b], yk, yv, BlackFork[c, zk, zv, d]]
  def balance(* in [RedFork[RedFork[a, xk, xv, b], yk, yv, c], zk, zv, d]) =
    RedFork[BlackFork[a, xk, xv, b], yk, yv, BlackFork[c, zk, zv, d]]
  def balance(* in [RedFork[a, xk, xv, RedFork[b, yk, yv, c]], zk, zv, d]) =
    RedFork[BlackFork[a, xk, xv, b], yk, yv, BlackFork[c, zk, zv, d]]
  def balance(* in [a, xk, xv, RedFork[b, yk, yv, RedFork[c, zk, zv, d]]]) =
    RedFork[BlackFork[a, xk, xv, b], yk, yv, BlackFork[c, zk, zv, d]]
  def balance(* in [a, xk, xv, RedFork[RedFork[b, yk, yv, c], zk, zv, d]]) =
    RedFork[BlackFork[a, xk, xv, b], yk, yv, BlackFork[c, zk, zv, d]]
  def balance(* in [a, xk, xv, b]) =
    BlackFork[a, xk, xv, b]
end