-- Homework 21, challenge: Swap.
--
-- Define `local function swap(a, b)` that returns b, a (two values).
-- Then:
--   1. Declare two variables x and y with starting values.
--   2. Print "Before:" with the values.
--   3. Use multi-assignment to capture swap(x, y) back into x and y.
--   4. Print "After:" with the new values.
--
-- Run with: lua exercises/21/homework/04-swap.lua

-- Your code goes here: