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list = [1, 2, 3, 4]
list_ = [x | x <- list, even (2*x)] -- [1, 2, 3, 4]
list__ = [x | x <- list, even x || odd x] -- [1, 2, 3, 4]
odds = [x | x <- list, odd x] -- [1, 3]
mul3s = [3*x | x <- list] -- [3, 6, 9, 12]
allCombinations = [(y, x) | x <- list, y <- list] -- [(1, 1), (1, 2)