x . x): Int -> Int Bool -> Bool (a->b) -> (a->b)but any valid type will be an instance of the principal type: a -> a. An instance is derived by substituting the same type expression for all occurences of some {type variable}. The principal type of an expression can be computed from those of its subexpressions by Robinson's unification algorithm.(1994-12-16)algorithm.(1994-12-16)……">