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4.4 Ordered structures (10 pts) 1. Consider a list A deployed as a data structure to implement the Queue Abstract Data a Type. Define operations enqueue (A, el) and dequeue (A) where the head of A corresponds to the front of the Queue. 2. Assume that function concat did not exist. Construct your own version of concat(A1, A2) for lists A1,2, and unfold the definition for concat((a, b), (c,d))