# Exercise 1.41

Here is the `double`

procedure.

Using the substitution model:

```
(((double (double double)) inc) 5)
(((double (lambda (x) (double (double x)))) inc) 5)
(((lambda (x) (double (double (double (double x))))) inc) 5)
((double (double (double (double inc)))) 5)
```

In the last line itโs clear that the `inc`

procedure is applied \(2^4\) times so the final result is `5`

.