Make the aliasing bug impossible

A Team object was leaking its internal roster. Implement a leak-proof version: 1. static final class Team with a List<String> members field 2. Constructor takes List<String> initial and defensively copies it 3. add(String m) appends; members() returns an UNMODIFIABLE view 4. static List<String> freeze(List<String> src) returns a copy that the caller can then mutate without ever affecting any Team Tests attempt both leak directions: outside-in (mutating the list after the ctor) and inside-out (mutating the returned view).

Difficulty: advanced