examples
[1 2 3 4] [head... last] [head last] crouch --> [1 2 3] 4
[1 2 3 4] [first tail...] [first tail] crouch --> 1 [2 3 4]
[1 2 3 4] [head middle... last] [head middle last] crouch --> 1 [2 3] 4
[1 2 3 4] [first second rest...] [first second rest] crouch --> 1 2 [3 4]
[1 2 3 4] [head... next2last last] [head next2last last] crouch --> [1 2] 3 4