Modify the recursive Fibonacci program given in the chapter so that it prints tracing information. Specifically, have the function print a message when it is called and when it returns. For example, the output should contain lines like these:
Computing fib(4)
...
Leaving fib(4) returning 3
Use your modified version of fib to compute fib(10) and count how many times fib(3) is computed in the process.