Implement a tail-recursive function find that takes as arguments a function predicate and a list l and returns either a pair index-element or #f. The implementation must only use the list constructors and selectors that we covered in our class. The objective of the function is to find a index-element in a list given some predicate. Function find calls function predicate over each element of the list until the predicate returns true. If predicate returns true, then function find returns a pair with the zero-based index of the element and the element.