unlock the door. >> okay. >> so if you were to do this in sort of a very natural, methodical method, you'd put in 0-0-0, you'd put in 0-0-1. >> make your way through. >> and you test every number from 0 to 9-9-9, okay, and that might take you a while. >> and that's 1,000 codes, and i have to hit -- for each code, i hit it three times, so that's 3,000 pushes, right? >> exactly. okay, now, if you use something called a de bruijn sequence, okay, this is a way of organizing this information so we really reduce the amount of work that we're going to do. we're going to cut the amount of work by a factor of 10. in a de bruijn sequence, we can organize the list of numbers in such a way that every three digits that we want to read is a different set, a different combination. so you might start with 0-0-0, test those first three, and then hit 1, that's going to be 0-0-1 is now going to be tested. >> i see, so i'm sort of sliding a window along.