Project 4 help

I have done part of Task 2 and came up with a varsubst function which looks
like:

(defun varsubst (pattern binding)
(if (null pattern) nil
(if (atom (car pattern))
(if (eq '? (car pattern)) ;find matching and return var
;if pattern is (? var)
(if (equal pattern (caar binding)) (list (cadar binding))
;if binding doesn't match, traverse through bindings
(list (match-var pattern (rest binding))))
;else, atom in pattern isn't ?, so append car pattern to return list
(append (list (car pattern))
(varsubst (rest pattern) binding)))
;else, not an atom...pattern is a list
(append (varsubst (car pattern) binding) (if (null (varsubst (rest
pattern) binding)) nil (list(varsubst (rest pattern) binding)))))))

(defun match-var (pattern binding)
(if (equal pattern (caar binding)) (cadar binding) (match-var pattern (rest
binding))))

I'm not sure if it is supposed to look that customized, but it works.

I am now on the rename function and understand that the same generated number
suffix is appended to each variable. I can generate a number such as "112"
but it is in String format. I've been looking around and can't figure out how
to combine "112" and 'rao to produce a variable like 'rao112.

Thanks in advance.