public string deletePost(string forumName, string subForumName, int postNo, string requestingUser)
        {
            List <string> input = new List <string>()
            {
                forumName, subForumName, requestingUser
            };

            if (Constants.isValidInput(input))
            {
                lock (o)
                {
                    postDeletionPermission pdp = _fm.getForumPostDeletionPermission(forumName);
                    if (pdp == postDeletionPermission.INVALID)
                    {
                        return(Constants.noPermissionToDeletePost(requestingUser));
                    }
                    permission p = _um.getUserPermissionsForSubForum(forumName, subForumName, requestingUser);
                    if (p == permission.INVALID)
                    {
                        return(Constants.noPermissionToDeletePost(requestingUser));
                    }
                    return(_fm.deletePost(forumName, subForumName, postNo, pdp, p, requestingUser));
                }
            }
            return(Constants.INVALID_INPUT);
        }