I'm trying to understand the technique referred to as "tying the knot", but documentation on the internet seems to be much sparser and more obtuse than I like. So I'm asking here. As far as I understand, "tying the knot" refers to a way of using laziness to implement something like references in a purely functional way. I'm trying to write a toy simulation: I have a population :: [Person] I want to collect a random subset of possible pairs of distinct people. So I go to each person in the population and select a subset of the people after him/her in the list; these are pairs in which s/he is the first element. I want to then be able to ask for all pairs in which a person is the first or the second element. I could give each person a unique id, but it seems like tying the knot is a valid way to implement this. Please correct me if I am misunderstanding. Thank you. -- Alex R