For problem 4 in the euler project part of the assignment is to generate a list of products of 3-digit numbers.
The easy way is to just do a cartesian product (I think it's called), and after that find the largest value that is a palindrome.
My question is, is it possible to generate a list of pairs of which the product is ordered?
For example with 2-digits:
99,99 99,98 98,98 99,97 98,97 etc..
My attempt is (in haskell):
productsOf2Digits = productsOf2Digits' 99 99 productsOf2Digits' 90 90 = (90,90, 90*90) :  productsOf2Digits' a b | a == b = (a,b,a*b) : productsOf2Digits' 99 (b-1) | otherwise = (a,b,a*b) : productsOf2Digits' (a-1) b
(99,99,9801) (99,98,9702) (98,98,9604) (99,97,9603) (98,97,9506) (97,97,9409) (99,96,9504) (98,96,9408) (97,96,9312) (96,96,9216)
99 96 breaks the ordering.
I think maybe I can exploit that the differences should be increasing?
Also, might it have to do with? http://www.cs.ox.ac.uk/people/jeremy.gibbons/publications/rationals.pdf