old_contents: def listPrimes(n):
  	'''Returns a list of primes below n.'''
  	numbers = set(range(n, 1, -1))
  	primes = []
  
  	while numbers:
  		p = numbers.pop()
  		primes.append(p)
  		# Remove each multiple of p from numbers:
  		numbers.difference_update(set(range(p * 2, n + 1, p)))
  	return primes
  
new_contents: def listPrimes(n):
  	'''Returns a list of primes below n.'''
  	numbers = set(range(2, n + 1))
  	primes = []
  
  	while numbers:
  		p = numbers.pop()
  		primes.append(p)
  		# Remove each multiple of p from numbers:
  		numbers.difference_update(set(range(p * 2, n + 1, p)))
  	return primes
  
subject: Update primes.py