Thanks, Corion. Your reply made me realize that I'm actually doing the substitutions multiple times on the same strings. If I have a list of 10 strings, I compare the first one with the second one, then the third, etc. until the end, then repeat starting with the second string and compare it to the third, and so on. So instead of doing the substitution multiple times, I'll do it once, store the results in a new variable used for comparison only, and I'll use the real value when it's time to write something. Brilliant! I could also probably improve the algorithm itself, but if I stop doing the substitution multiple times on the same string, I should get an acceptable execution time. And thanks for the tip about Memoize! I'm sure that this one will be handy in some other cases. Have a great day! TA