Task
📝 **Task:** Predict the exact output. \`Permission\` has READ=1, WRITE=2, EXECUTE=4, DELETE=8 (auto-assigned powers of 2). Trace through union, \`in\` checks, subtract-via-\`& ~\`, and iteration.
📋 Implement the function above. Tests run automatically.
💡 **Hint:** Re-read the theory if you get stuck.