(Due Date: Wednesday 10th, March)

Question 1:

Write a function sublist which receives two list and return true if the 
first list is a sublist of the second, or false otherwise.
(In lists the order is important, thus for example [2,4,5] is a sublist
of [3,7,2,4,5,9] but not [3,7,4,2,5,9]).

Question 2:

Write a function subtree  which receives two binary trees and return true if the
first tree is a subtree of the second, or false otherwise.

(In trees the structure is important, thus a tree could be a subtree in 
any place).

  For this function you have to use the following datatype:

- datatype tree = Empty |
                  Leaf of int |
                  Node of int*tree*tree;

Example:

- val tree1 = Node(3,Leaf(5),
                    Node(6,Leaf(7),Leaf(4))
                 );

        3
       / \
      5   6
         / \
        7   4


- val tree2 = Node(13,Node(3,Leaf(5),
                            Node(6,Node (7, Leaf (2), Empty),
                                  Node(4,Leaf(3),Leaf(4))
                                )
                        ) ,
                    Node(12,Leaf(9),
                            Node(6,Leaf(11),Leaf(7))
                        )
                 );


           13
         /    \
        3      12
       / \     / \ 
      5   6   9   6
         / \     / \
        7   4   11  7
       /   / \
      2   3   4

- subtree(tree1,tree2);
> true