{lib, ...}: rec {
  min = a: b: if a < b then a else b;
  max = a: b: if a > b then a else b;
  # build list of `len` lists of `n` elements of `xs`
  windows = with builtins; n: xs: let
    len = length xs;
    n' = min n len;
    # when len = n, there is still one window
    num-windows = max 0 (len - n' + 1);
  in
    genList
      # for i in 0..len
      (i: genList
        # for j in 0..n -> xs[i + j]
        (j: elemAt xs (i + j))
        n')
      num-windows;

  isEmptySet = set: with builtins; length (attrNames set) == 0;
}