# Bidding theorems
Anecdotal bridge-bidding principles and observations, jotted as they come up.
Not authored conventions — raw theory. Promote one into the system (or the
AI-bidder corpus) when it earns its keep.
- The [useful space principle](https://en.wikipedia.org/wiki/Useful_space_principle)
is an axiom for allocating meaning to calls: spend cheaper bids on the more
frequent / more space-needing meanings.
- Whenever there is a debate between forcing and non-forcing responses, choose
transfer responses!
- I summarize [Terrorist’s article](https://www.ptt.cc/man/BridgeClub/D6D1/D49B/D823/M.1042682810.A.3EF.html) on generalized Rubens advances
- Direct XX somehow bears the meaning of natural notrump. Consider using NT as a
cuebid to X.
- Suit-selection style is a *partnership-wide inference contract*: every rule of
the form "with two biddable suits, bid X first" is also a promise partner
reads. Our minor-opening responses over-apply up-the-line beyond 4-4 — the
1♥ rule fires on any four-plus hearts, so 5♠4♥ and 6♠5♥ respond 1♥
(`minor_responses`, `responses.rs`) — which breaks longest-first inference
and forced the M6.4 control-bid classifier to read `1♣–1♥–2♣–4♠` as natural
(the naive "shown another suit ⟹ can't be longest" reading lost 6 IMPs per
fired board on real 6♠5♥ traffic). The 1NT/2NT transfer tables had the same
disease and were fixed (`set_transfer_longer_major`: transfer the longer
major; equal 5-5 splits weak→hearts, INV/min-FG→3♦, slam-try→spades).
Promoting longest-first into the minor-opening responses must move three
things together: the response rule, the rebid structure it implies, and the
classifier's bypass rule — piecemeal changes desynchronize bidder and
reader. Built as that trio in `set_longer_major_response` (response pair in
`minor_responses`, opener's `1♠` rebid under `set_up_the_line`, and the
discipline-gated bypass swap in `classify_high_bid`) and measured by
`ab-minor-continuations` (2026-07): a **null** — plain-DD wash alone, and a
small consistent *negative* marginal (−0.003..−0.005 IMPs/board) on top of
the shipped xyz + up-the-line package. The lesson: opener's up-the-line
`1♠` rebid recovers the concealed 4-4 spade fits more cheaply than
re-siding the response, and longest-first pays a level on the heart fits.
Hearts-first stays the default; the knob remains opt-in.
- **An authored node must not be more conservative than the floor it
shadows** — and the floor is more aggressive than the textbook. Over
`1M–3M` (limit raise, 9-card fit known) the instinct floor's raise-partner
ladder accepts at **13+** points, and A/Bs of textbook accepts at 14 (then
15) lost −4.6/−5.2 IMPs per divergent board vulnerable: *every* divergent
board was the authored table stopping in 3M where the floor's game made
(2026-07-04, `probe-limit-raise`). DD prices a known nine-card fit at 23
combined as a clear game. Two lessons: (1) before authoring a node, probe
what the floor actually does there (`probe-classify` prints the winning
rule and logits) — the milestone rules are not the whole floor, the
raise-partner ladder also fires; (2) game acceptance with a big fit is a
point *cheaper* than hand-evaluation folklore says. Untested residual: a
12-point accept would *out*-bid the floor — measure before believing
either way.