I am new to Scheme; I am writing a program that recursively defines multiplication in terms of repeated addition:

```
(define multiply 
  (lambda (a b) 
    (if (= b 0) 
        0 
        (+ a (multiply(a, (- b 1)))))))

```

However, when I attempt to run the program I am getting the error message:

```
;Unbound variable: unquote

```

What is the error message referring to, and how can I rectify it?