code: @Override
      public T put(int x, int y, int z, T value) {
          long key = Int21TripleHashed.key(x, y, z);
          return map.put(key, value);
      }
docs: Associates the specified value with the specified key in this map (optional operation). If the map previously contained a mapping for the key, the old value is replaced by the specified value.
  (A map m is said to contain a mapping for a key k if and only if {@see #containsKey(int, int, int) m.containsKey(k)} would return <code>true</code>.)
  
  @param x an <code>int</code> value
  @param y an <code>int</code> value
  @param z an <code>int</code> value
  @return the previous value associated with <code>key(x, y, z)</code>, or no_entry_value if there was no mapping for <code>key(x, y, z)</code>. (A no_entry_value return can also indicate that
  the map previously associated <code>null</code> with key, if the implementation supports <code>null</code> values.)