| RCanL : forall a , Arrange ( [],,a ) ( a )
| RCanR : forall a , Arrange ( a,,[] ) ( a )
| RuCanL : forall a , Arrange ( a ) ( [],,a )
| RCanL : forall a , Arrange ( [],,a ) ( a )
| RCanR : forall a , Arrange ( a,,[] ) ( a )
| RuCanL : forall a , Arrange ( a ) ( [],,a )