Taixuanjing (81 Tetragrams) (太玄經)

Yang Xiong's Canon of Supreme Mystery (2 BCE) — the Han dynasty's deliberate counter-canon to the I Ching: 81 TERNARY tetragrams (four lines of heaven/earth/man) in place of 64 binary hexagrams. The received sequence IS base-3 counting (中 #1 = 1·1·1·1 … 養 #81 = 3·3·3·3, a law asserted at load), the four lines read top-down as the text's own 方 region · 州 province · 部 department · 家 family hierarchy (3→9→27→81), and each 首 carries 9 appraisals (贊) — two to a day-and-night, so the 729 appraisals span 364½ days from the WINTER SOLSTICE where 中 opens the yang breath, closed by the intercalary 踦 and 嬴 appraisals to the quarter-remainder calendar's 365¼. Query by tetragram number, by four cast lines, or by date (the governing 首 of the Taixuan year, anchored to the real astronomical solstice — the summer solstice provably lands in 應 #41, the all-earth midpoint). Names double-sourced: the received text ≡ the Unicode Tai Xuan Jing block with Nylan's canonical translations. The full 準 hexagram correspondence table is deferred, not guessed.

Cost: 2 TIAN Points per call. tRPC procedure taixuan.compute.