CHECK for 2 FKs to be non equal

Good morning,

I am trying to add a table holding player reviews of each other:

words=> CREATE TABLE words_reviews (
uid integer NOT NULL REFERENCES words_users(uid) CHECK (uid <>
author) ON DELETE CASCADE,
author integer NOT NULL REFERENCES words_users(uid) ON DELETE
CASCADE,
nice boolean NOT NULL,
review varchar(255),
updated timestamptz NOT NULL,
PRIMARY KEY(uid, author)
);

but get syntax error in 9.5:

ERROR: syntax error at or near "ON"
LINE 2: ...REFERENCES words_users(uid) CHECK (uid <> author) ON DELETE ...
^

My intention is to forbid users to rate themselves by the CHECK (uid <>
author).

What am I doing wrong please?

Regards
Alex

P.S. I apologize if GMail misformats my message... Here is the words_users
table:

words=> \d words_users

Table "public.words_users"

Column | Type |
Modifiers

---------------+--------------------------+-----------------------------------------------------------

uid | integer | not null default
nextval('words_users_uid_seq'::regclass)

created | timestamp with time zone | not null

visited | timestamp with time zone | not null

ip | inet | not null

fcm | character varying(255) |

apns | character varying(255) |

vip_until | timestamp with time zone |

grand_until | timestamp with time zone |

banned_until | timestamp with time zone |

banned_reason | character varying(255) |

win | integer | not null

loss | integer | not null

draw | integer | not null

elo | integer | not null

medals | integer | not null

green | integer | not null

red | integer | not null

coins | integer | not null

Indexes:

"words_users_pkey" PRIMARY KEY, btree (uid)

Check constraints:

"words_users_banned_reason_check" CHECK (length(banned_reason::text) >
0)

"words_users_draw_check" CHECK (draw >= 0)

"words_users_elo_check" CHECK (elo >= 0)

"words_users_green_check" CHECK (green >= 0)

"words_users_loss_check" CHECK (loss >= 0)

"words_users_medals_check" CHECK (medals >= 0)

"words_users_red_check" CHECK (red >= 0)

"words_users_win_check" CHECK (win >= 0)

Referenced by:

TABLE "words_chat" CONSTRAINT "words_chat_uid_fkey" FOREIGN KEY (uid)
REFERENCES words_users(uid) ON DELETE CASCADE

TABLE "words_games" CONSTRAINT "words_games_player1_fkey" FOREIGN KEY
(player1) REFERENCES words_users(uid) ON DELETE CASCADE

TABLE "words_games" CONSTRAINT "words_games_player2_fkey" FOREIGN KEY
(player2) REFERENCES words_users(uid) ON DELETE CASCADE

TABLE "words_moves" CONSTRAINT "words_moves_uid_fkey" FOREIGN KEY (uid)
REFERENCES words_users(uid) ON DELETE CASCADE

TABLE "words_notes" CONSTRAINT "words_notes_uid_fkey" FOREIGN KEY (uid)
REFERENCES words_users(uid) ON DELETE CASCADE

TABLE "words_scores" CONSTRAINT "words_scores_uid_fkey" FOREIGN KEY
(uid) REFERENCES words_users(uid) ON DELETE CASCADE

TABLE "words_social" CONSTRAINT "words_social_uid_fkey" FOREIGN KEY
(uid) REFERENCES words_users(uid) ON DELETE CASCADE