A Weak Opening System by Lukasz Slawinski (and Stanislaw Ruminski) 1970, published in english as booklet in 1974. Regres is an improvement of the ANTIDELTA system (1969) . Hands with a HCP of 8-12 are the most common. The idea is that it will be better to open these hands instead of passing first and , if possible and not too risky, to overcall afterwards, because the opponent exchanged information already. The majority of the openingbids therefore is reserved for the 8-12 zone.To give the 13+ zone (with much more chance for a game or more) as much bidding space as possible (Fibonacci Numbers= number of bidding steps); the openingbid of Pass is therefore used. Finally the weak zone of 0-7: a fert, with the bid of 1

.
Biddingsequences are build according the principal of symmetric. Unbalanced shapes, that means with a singleton or void, have the priority regarding the first calls instead of mentioning your longest suit. Knowing the shortest suit gives more information than f.e. a 1 opening (5+ card) in a regular system of which the length of the other suits is fully unknown (from 0-5). In this way in Regres a balanced opening (from 4333 upto 7222) guarantees always a doubleton in each suit, A Singleton opening improves finding a playable fit, enables you immediately to evaluate the value of your longest suit, your honours and the ruff-possibilities.Captain in shortness openings will be in most cases therefore the balanced hand.
The final contract should be played by the leader of the auction that means the player who get first information about his partner's distribution and by the partner whose hand is stronger. In this way the dummy does not give any more information than already told; the opening lead will be done to the stronger hand; the majority of the honours will be covered.

Openings in 1st/2nd position
Bid	HCP	Description
[Pass]	13+	any shape
1	8-12	singleton/void any suit , shape 4441 up to 7330
1	0-7	any shape and no any Ace + King
1	8-12	3-4 card, no shortness, at most 4 (= longer or equal than) at most 5card minor, if 5332 then poor 5card
1	8-12	3-4 card, no shortness, at most 3 in case 3card + : choose best major at most 5card minor, if 5332 then poor 5 card
1	8-12	at least 5 card major, no shortness
2	8-12	at least 5card, no shortness, no major, if 5332 then good clubs
2	8-12	at least 5card, no shortness, no major, if 5332 then good diamonds
2	8-12	6 - 4 or 6 - 4 no 3card major (7-4 included) 5 - 5 or 5 - 5 no 3card major (6-5 or 6-6 incl.)
2	8-12	6 - 4 or 6 - 4 no 3card major (7-4 included) 5 - 5 or 5 - 5 no 3card major (6-5 or 6-6 incl.)
2	8-12	6 - 4 or 6 - 4 no 3card major (7-4 included) 5 - 5 or 5 - 5 no 3card major (6-5 or 6-6 incl.)
3	8-12	6 - 4 or 6 - 4 no 3card major (7-4 included)
3		up to you
3		up to you
3		up to you
3		up to you
4		strong pre-empt with
4		strong pre-empt with
4		up to you
4		up to you

To illustrate the basic structure of REGRES:

ANSWERS after [PASS] : you could better say “openings”
Bid	HCP	Description
[1]	6-11 11+ 12+	balanced with shortness any shape
1	0-5	any shape
1/ 2	6-10	singleton openings
2	6-11	closed 7-carder without a side Queen
2	6-8	7-carder with two high honours
3	6-8	7-carder with two high honours
3	6-8	7-carder with two high honours
3	6-8	7-carder with two high honours
3	6-8	any 8-carder with two high honours
3	8-12	closed 7-carder with a side Queen

Note:originally 3-3 were 6-8 natural 7 carder with 2 high honours
and 2 (if you use Delta singleton scheme) and 3 were open.
If you do not use the singleton Delta scheme 2= S and 5+
and 2 =S and 5/5

Sequence : [PASS] - [1] - ?
Bid	HCP	Description
[1]	13-18 19+ 18+	balanced any shape with shortness
1/ 2	13-17	singleton openings
2		up to you (if no Delta scheme then S and 5+)
2		up to you (if no Delta scheme then S and 5/5)
3	13-15	natural very good 7-carder
3	13-15	natural very good 7-carder
3	13-15	natural very good 7-carder
3	13-15	natural very good 7-carder
3		up to you

Sequence : [PASS] - [1] - [1] - ?
Bid	HCP	Description
[1]	11+	any shape
1	6-11	balanced 4333, 4432
1	6-11	at least 5 carder, no shortness
2	6-11	at least 5 carder, no shortness
2	6-11	at least 5 carder, no shortness
2	6-9	at least 5 carder, no shortness
2	10-11	at least 5 carder, no shortness
2		up to you (if no Delta scheme then 11-13 4441)
3	10-11	7222
3	10-11	7222
3	10-11	7222
3	10-11	7222

Sequence : [PASS] - [1] - [1] - [1] - ?
Bid	HCP	Description
[1]	19+ 18+	any shape with shortness
1	13-18	balanced 4333, 4432
2	13-18	at least 5 carder, no shortness
2	13-18	at least 5 carder, no shortness
2	13-18	at least 5 carder, no shortness
2	13-18	at least 5 carder, no shortness

Through a relay-systeem you can ask for exact shape and strength within the pointrange in the Delta singleton scheme. Natural bidding style if no relay or breaking the relay in a forcing situation.
In shapes with no shortness: Relays- and natural bidding style.
For the 2-3 openings a relay system has been worked out.
Furthermore:
Jumping shortness convention; simple raise in partner's suit is stronger than a jump in a forcing situation; more relays= a more stronger hand; Endsignal.

Source:
Introduction to Weak Opening Systems and REGRES System
by Lukasz Slawinski & Stanislaw Ruminski, 5th edition, june 1979