code: @Override
      public void removeReaction(int pos) {
          for (int i = pos; i < reactionCount - 1; i++) {
              reactions[i] = reactions[i + 1];
          }
          reactions[reactionCount - 1] = null;
          reactionCount--;
      }
docs: Remove a reaction from this set.
  
  @param  pos  The position of the reaction to be removed.