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Answer to Question 33E-2

Here are the equations for reference. 
(cat.1)   cat([ ],  B) = B
(cat.3)   cat(A, B) = head(A) : cat(tail(A), B)

Evaluation is as follows.

   cat([1, 2, 3], [4, 5, 6])
     = 1 : cat([2, 3], [4, 5, 6])  by (cat.3)
     = 1 : (2 : cat([3], [4, 5, 6]))  by (cat.3)
     = 1 : (2 : (3 : cat([ ], [4, 5, 6])))  by (cat.3)
     = 1 : (2 : ([3, 4, 5, 6]))  
     = 1 : ([2, 3, 4, 5, 6])  
     = [1, 2, 3, 4, 5, 6]