
  [;1m-spec composite(Function1, Function2) -> Function3[0m
  [;1m                   when[0m
  [;1m                       Function1 :: a_function(),[0m
  [;1m                       Function2 :: a_function(),[0m
  [;1m                       Function3 :: a_function().[0m

  Returns the composite of the functions [;;4mFunction1[0m and [;;4mFunction2[0m.

    1> F1 = sofs:a_function([{a,1},{b,2},{c,2}]),
    F2 = sofs:a_function([{1,x},{2,y},{3,z}]),
    F = sofs:composite(F1, F2),
    sofs:to_external(F).
    [{a,x},{b,y},{c,y}]
