2008/4/28 cetin tozkoparan <cetintozkoparan@yahoo.com>:

Assume a tree is a subtree of the other if all elements of the first tree is included in the second with the exact structure; all parent-child relations are preserved with their order.

data Tree = Empty | Leaf Int | Node (Int,Tree,Tree)
subtree:: Tree -> Tree -> Bool

Let me also point out that since you store an Int at each Node, there is no need for the explicit Leaf constructor; for example, Leaf 5 can be represented as Node 5 Empty Empty. Simplifying your data structure in this way will make writing code for it much simpler and more elegant.

-Brent