[racket] racket newbie question on quoting and the built in procedure-arity function

Hello,

I am working with functions that I have defined to only take 1 or 2
operands (called safe-functions) for the implementation of a genetic
program.

(define ($+ augend addend) ;operation is addition
  (+ augend addend)) ; the result is the sum
(define ($- minuend subtrahend) ;operation is subtraction
  (- minuend subtrahend)) ;result is difference
(define ($* multiplicand multiplier) ;operation is multiplication
  (* multiplicand multiplier)) ;result is product
(define ($/ dividend divisor) ;operation is division
  (/ dividend divisor)) ;result is quotient

(define (infinity? x) (or (eq? x +Inf.0) (eq? x -Inf.0)))
(define ($sin x) (if (infinity? x) (* (sgn x) +Inf.0) (sin x)))
(define ($cos x) (if (infinity? x) (* (sgn x) +Inf.0) (cos x)))

(define safe-function-set
  '($+
    $-
    $*
    $/
    ;$sin
    ;$cos))

(define (select-random-safe-function)
  (list-ref safe-function-set (random (length safe-function-set))))

I would like to use procedure-arity (or a similar function) to determine
the arity of a randomly selected safe function but I get this error:

>(procedure-arity (select-random-safe-function))
error: procedure-arity: contract violation
  expected: procedure?
  given: '$+

*I think the problem is that the safe-functions are passed to
procedure-arity quoted. Is there a way I can unquote the functions, or
adjust procedure-arity to make (procedure-arity
(select-random-safe-function)) work?*

Thanks,
-- 
Rian Shams
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