def factors(n):
  if n==1:
    return []
  for i in justprimes(n+1):
    if div(n, i): return ([i] + factors(n/i))

def simplify(n,d):
  for i in factors(n):
    if div(d, i):
      d=d/i
      n=n/i
  return str(n)+'/'+str(d)