foldlOL k z (Two b1 b2) = let !z' = (foldlOL k z b1) in foldlOL k z' b2
foldlOL k z (Two b1 b2) = let !z' = (foldlOL k z b1) in foldlOL k z' b2
foldlOL k z (Two b1 b2) = let !z' = (foldlOL k z b1) in foldlOL k z' b2