What operations does a deque support?

A deque (double-ended queue) supports the following main operations, all in O(1):

1. addFront(x): add element x to the front.
2. addRear(x): add element x to the back.
3. removeFront(): remove and return the element from the front.
4. removeRear(): remove and return the element from the back.
5. peekFront(): look at the first element without removing it.
6. peekRear(): look at the last element without removing it.
7. isEmpty(): check whether the queue is empty.
8. size(): return the number of elements (sometimes added).

Thanks to access from both sides, a deque can be used both as a queue (FIFO) and as a stack (LIFO).