code: @Override
      public boolean remove(Object key, Object value) {
          return rMap.remove(key, value);
      }
docs: Removes the entry for a key only if currently mapped to a given value.
  This is equivalent to
  <pre>
  if (map.containsKey(key) &amp;&amp; map.get(key).equals(value)) {
  map.remove(key);
  return true;
  } else return false;</pre>
  except that the action is performed atomically.
  
  @param key key with which the specified value is associated
  @param value value expected to be associated with the specified key
  @return <tt>true</tt> if the value was removed
  @throws UnsupportedOperationException if the <tt>remove</tt> operation
  is not supported by this map
  @throws ClassCastException if the key or value is of an inappropriate
  type for this map
  (<a href="../Collection.html#optional-restrictions">optional</a>)
  @throws NullPointerException if the specified key or value is null,
  and this map does not permit null keys or values
  (<a href="../Collection.html#optional-restrictions">optional</a>)