Siege

1H/S = 5+cards, rule of 19

"Siege Light" is so called because it features light 2/1 responses and light major suit openings. It is particularly suitable for those who are more comfortable with Acol than 2/1 GF.

Responses -
1N 6-9, denies 3 card support. 2N rebid by responder = good raise
2X 10+, forcing to 2 of opener's major

After a 2/1 response -

• A 2N rebid by opener = GF single suiter
• Raising responder's suit = NF
• The step above 3 of responder's suit = GF raise
• 3M = splinter in the suit "lost" to the GF raise - e.g. 1H:2C, 3H = diamond splinter
  
• 3N = 17-19.

Follow-ups usually natural at 3 level, cues at 4 level. After 1S:2X, 2N, responder's bids are natural (3S from either side sets spades as trumps) and 4th suit forcing applies. 1S:2C, 2N:3D, 4C:4S is to play, not a cue (responder may be 2245 unsure of best game). After a 3N rebid - 4C asks for suitability for slam in responder's suit (4D = unsuitable, others = cues); 4 of responder's suit = two-suiter, clubs+first bid suit, forcing; 4S to play, 4N quant.

There is some merit in using 2/1 GF in response to 1H and light 2/1s in response to 1S. This is because 2/1 makes the 1S:1NT sequence very unwieldy - 1H:1NT, 2m:2S is free to be a good raise which allows weaker hands to raise directly to 3m, whereas after 1S:1NT there is only one way to raise opener's minor.