The encoding ladder presents one execution in four machine-readable forms. E0 is canonical Brainfuck with implicit pointer-relative operands. E1 applies a per-item symbol permutation and supplies an operational legend. E2 is a compact, explicit-address instruction stream. E3 preserves the explicit operations but uses verbose lexemes. E4 is not an official rung.
T1 asks for machine state at an interior execution step. T2 asks for a restricted arithmetic expression observationally equivalent to the program over the complete input domain. T3 asks for the output after a specified causal mutation. T4–T6 are schema reservations only.
N* is an interpolated trace length at which accuracy reaches 50% within a task family and experimental condition. It is undefined until suitable external-run observations exist; benchfck currently publishes none.
ρ (rho) is a normalized efficiency quantity stored separately from exact correctness and token counts. It must not be merged with task accuracy into a single leaderboard number.
Abstraction gain measures compression only for a correct T2 response, comparing the restricted expression representation with the represented computation. It is conditional on correctness and is never used to rescue an incorrect answer.
Avalanche is the fraction of eligible semantic-operation mutations that change the program's observed output. The configured candidate-acceptance floor is 0.60, with at least 64 sampled positions when full enumeration is not used.
Trace semantic density is the share of executed E0 steps that are not pointer movement. Source-text semantic density is the share of E0 source characters that are not movement characters. Their configured floors are 0.30 and 0.35 respectively.
The T2 hybrid nontriviality gate combines bottom-up observational enumeration through a measured, genuinely exhausted AST depth with analytical family tests that must synthesize a concrete parser-valid witness below the folded-expression token threshold. It does not claim global minimality and is currently available only for arity 1.