findLeafB u (Black4Zip v l r c)
  | u < v     = findLeafR u . toRedZip l $ BlackCrumb v (Left r) c
  | otherwise = findLeafR u $ toRedZip r $ BlackCrumb v (Left r) c
findLeafB u (Black4Zip v l r c)
  | u < v     = findLeafR u . toRedZip l $ BlackCrumb v (Left r) c
  | otherwise = findLeafR u $ toRedZip r $ BlackCrumb v (Left r) c
findLeafB u (Black4Zip v l r c)
  | u < v     = findLeafR u . toRedZip l $ BlackCrumb v (Left r) c
  | otherwise = findLeafR u $ toRedZip r $ BlackCrumb v (Left r) c