Decimal inspection with mathematical guarantees

Comparison agrees with exact extended rational order and ignores cohorts. Classification agrees with numerical zero and normal/subnormal thresholds. Total ordering distinguishes complete datums, with transitivity, totality, antisymmetry, signed-zero/cohort tie rules and NaN ordering proofs. Stored sign operations preserve all non-sign bits, including redundant encodings, and decoding commutes with sign replacement.

Neighbor operations and integer, format, and character conversions have their own proofs in Neighbors, Conversion, and Formatting.