logic-foundations / Finite model theory; descriptive complexity

The Blass-Gurevich-Shelah conjecture: choiceless polynomial time with counting does not capture polynomial time

Main theorem: over a fixed vocabulary of eight binary relations, consistency over F3\mathbb F_3 of an explicitly defined linear system (normalisation equations ∑a∈Xtλa=1\sum_{a\in X_t}\lambda_a=1 and consistency equations μy=∑a∈XtλaC(y,a)\mu_y=\sum_{a\in X_t}\lambda_aC(y,a)) is a polynomial-time query on all finite structures, with no promise, that no CPT program with counting defines, allowing hereditarily finite sets of unbounded rank. Priority: Shelah (2000) claimed noncapture for counting extensions of choiceless computation; later accounts kept the problem open, and the manuscript gives a separate proof not relying on that claim. Not shown: Gurevich's conjecture that no logic captures polynomial time, or anything about rank-based or other extensions.

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logic-foundationsSep 23, 2026Significance 42/100Registry: lean checked

The Blass-Gurevich-Shelah conjecture: choiceless polynomial time with counting does not capture polynomial time

Prior state unknown→proved

Main theorem: over a fixed vocabulary of eight binary relations, consistency over F3\mathbb F_3 of an explicitly defined linear system (normalisation equations ∑a∈Xtλa=1\sum_{a\in X_t}\lambda_a=1 and consistency equations μy=∑a∈XtλaC(y,a)\mu_y=\sum_{a\in X_t}\lambda_aC(y,a)) is a polynomial-time query on all finite structures, with no promise, that no CPT program with counting defines, allowing hereditarily finite sets of unbounded rank…

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Main theorem: over a fixed vocabulary of eight binary relations, consistency over F3\mathbb F_3 of an explicitly defined linear system (normalisation equations ∑a∈Xtλa=1\sum_{a\in X_t}\lambda_a=1 and consistency equations μy=∑a∈XtλaC(y,a)\mu_y=\sum_{a\in X_t}\lambda_aC(y,a)) is a polynomial-time query on all finite structures, with no promise, that no CPT program with counting defines, allowing hereditarily finite sets of unbounded rank. Priority: Shelah (2000) claimed noncapture for counting extensions of choiceless computation; later accounts kept the problem open, and the manuscript gives a separate proof not relying on that claim. Not shown: Gurevich's conjecture that no logic captures polynomial time, or anything about rank-based or other extensions.

Main theorem: over a fixed vocabulary of eight binary relations, consistency over F3\mathbb F_3 of an explicitly defined linear system (normalisation equations ∑a∈Xtλa=1\sum_{a\in X_t}\lambda_a=1 and consistency equations μy=∑a∈XtλaC(y,a)\mu_y=\sum_{a\in X_t}\lambda_aC(y,a)) is a polynomial-time query on all finite structures, with no promise, that no CPT program with counting defines, allowing hereditarily finite sets of unbounded rank. Priority: Shelah (2000) claimed noncapture for counting extensions of choiceless computation; later accounts kept the problem open, and the manuscript gives a separate proof not relying on that claim. Not shown: Gurevich's conjecture that no logic captures polynomial time, or anything about rank-based or other extensions.

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The Blass-Gurevich-Shelah conjecture: choiceless polynomial time with counting does not capture polynomial time — Mathematical Frontier Network