README.md in trackler-2.2.1.136

- old
+ new

@@ -3,12 +3,12 @@
 Use the Sieve of Eratosthenes to find all the primes from 2 up to a given
 number.
 
 The Sieve of Eratosthenes is a simple, ancient algorithm for finding all
 prime numbers up to any given limit. It does so by iteratively marking as
-composite (i.e. not prime) the multiples of each prime,
-starting with the multiples of 2.
+composite (i.e. not prime) the multiples of each prime, starting with the
+multiples of 2. It does not use any division or remainder operation.
 
 Create your range, starting at two and continuing up to and including the given limit. (i.e. [2, limit])
 
 The algorithm consists of repeating the following over and over:
 
@@ -23,10 +23,12 @@
 The wikipedia article has a useful graphic that explains the algorithm:
 https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes
 
 Notice that this is a very specific algorithm, and the tests don't check
 that you've implemented the algorithm, only that you've come up with the
-correct list of primes.
+correct list of primes. A good first test is to check that you do not use
+division or remainder operations (div, /, mod or % depending on the
+language).
 
 ## Exception messages
 
 Sometimes it is necessary to raise an exception. When you do this, you should include a meaningful error message to
 indicate what the source of the error is. This makes your code more readable and helps significantly with debugging. Not