Next, we will use a binary tree structure defined with two parameters. Such trees can be useful in various $(10)$

practical scenarios. A simple case is the representation of arithmetic operations. Here, the leaf nodes

are of a numeric type while the internal nodes hold the arithmetic operations.

type $(\text{'}$a$,\text{'}$b$)$ tree $=$

$|$ Leaf of $\text{'}$a

$|$ Tree of $(\text{'}$a$,\text{'}$b$)$ node

and

$(\text{'}$a$,\text{'}$b$)$ node $=\{$

operator: $\text{'}$b;

left: $(\text{'}$a$,\text{'}$b$)$ tree;

right: $(\text{'}$a$,\text{'}$b$)$ tree

$\}$;;