_inputs: _final: prev: let
  inherit
    (prev.lib)
    filter
    foldl'
    genAttrs
    genList
    mergeAttrs
    mkMerge
    stringToCharacters
    substring
    unique
    ;

  # Counts how often each element occurrs in xs.
  # Elements must be strings.
  countOccurrences =
    foldl'
    (acc: x: acc // {${x} = (acc.${x} or 0) + 1;})
    {};

  # Returns all elements in xs that occur at least twice
  duplicates = xs: let
    occurrences = countOccurrences xs;
  in
    unique (filter (x: occurrences.${x} > 1) xs);

  # Concatenates all given attrsets as if calling a // b in order.
  concatAttrs = foldl' mergeAttrs {};

  # True if the path or string starts with /
  isAbsolutePath = x: substring 0 1 x == "/";

  # Merges all given attributes from the given attrsets using mkMerge.
  # Useful to merge several top-level configs in a module.
  mergeToplevelConfigs = keys: attrs:
    genAttrs keys (attr: mkMerge (map (x: x.${attr} or {}) attrs));

  # Calculates base^exp, but careful, this overflows for results > 2^62
  pow = base: exp: foldl' (a: x: x * a) 1 (genList (_: base) exp);

  hexLiteralValues = {
    "0" = 0;
    "1" = 1;
    "2" = 2;
    "3" = 3;
    "4" = 4;
    "5" = 5;
    "6" = 6;
    "7" = 7;
    "8" = 8;
    "9" = 9;
    "a" = 10;
    "b" = 11;
    "c" = 12;
    "d" = 13;
    "e" = 14;
    "f" = 15;
    "A" = 10;
    "B" = 11;
    "C" = 12;
    "D" = 13;
    "E" = 14;
    "F" = 15;
  };

  # Converts the given hex string to an integer. Only reliable for inputs in [0, 2^63),
  # after that the sign bit will overflow.
  hexToDec = v: foldl' (acc: x: acc * 16 + hexLiteralValues.${x}) 0 (stringToCharacters v);
in {
  lib =
    prev.lib
    // {
      inherit
        concatAttrs
        countOccurrences
        duplicates
        hexToDec
        isAbsolutePath
        mergeToplevelConfigs
        pow
        ;
    };
}