What is Liu Yao (六爻)?
The same sixty-four figures, asked a different question — and the East Asian method Bokki has not built.
The idea
Liu Yao (六爻 · 육효, “six lines”) uses the same sixty-four figures as the I Ching but puts them to a different job. Where the classical Book of Changes reads a figure as an image and asks what it means, Liu Yao asks whether a particular thing will happen and roughly when. It is the working diviner's method — less philosophy, more casework. Tradition credits it to Jing Fang (京房) in the Han dynasty, and its machinery is called 납갑 (納甲), “taking in the stems”.
How the tradition calculates it
You cast a hexagram, and then you load it. 납갑 gives each of the six lines a heavenly stem, an earthly branch and therefore a five-element value, fixed per trigram. 세응 (世·應) marks one line as you and one as the other party, decided by where the figure sits in the eight-palace arrangement (팔궁 배괘). 육친 (六親) then labels every line parent, sibling, offspring, wealth or officer, by comparing its element with the palace's element. Finally you choose a 용신 (用神) — the one line your question is actually about — and judge it against the moving lines, against the branch of the day and of the month, and against 공망 (emptiness) and 형충 (clash), to reach both an answer and a timing.
What Bokki calculates: nothing — and precisely what is missing
We would rather be exact than vague about this. The engine already holds the parts the schools share: the sixty-four figures, all sixty-four judgments and all three hundred and eighty-four line texts, and two ways of casting — 매화역수 and the yarrow-stalk 시초점. What it does not hold is Liu Yao itself — and that missing comes in two kinds. Two pieces are tables we simply do not have: there is no 납갑 stem-and-branch table for the eight trigrams, and no eight-palace arrangement to place 세응 and hand a figure its palace element. Both are tables we would have to source and cross-check across editions before we trusted them, and we have not done that work. The rest needs stating carefully, because this site uses two of those words elsewhere, and a page that reads as more modest than the truth is no more honest than one that brags. The five-way comparison that 육친 is read from — same element, what generates it, what it generates, what it controls, what controls it — is already in the engine and runs on every reading; what is missing here is both of its inputs, a line's element and a palace's element, so no line on this site is ever labelled 父母 or 官鬼. Bokki does pick a 용신, but the Saju one, the element a chart is short of, not Liu Yao's chosen line. And Bokki does have timing, 대운 and 세운, which time a life rather than an event, so they are not 응기 either.
And one reason that is not a missing table
Liu Yao is built to answer “will it happen, and when”. Bokki has committed the other way: a reading describes flow and tendency, and we do not put a verdict on an outcome or on another person's choice. So building Liu Yao would put a real choice in front of us — ship the method as it actually is, or file its edges down until it is no longer the method. Filing the edges down and still calling it 육효 is the dishonest option, and it is the one we would be most tempted by. So it stays unbuilt, and this page says so, rather than a page that quietly lets you assume otherwise.
What you can do here instead
The part of this family Bokki does compute is the classical reading. You cast a hexagram by the yarrow-stalk method, you get the moving lines, and Zhu Xi's rule tells you which judgment or line text to read. It answers a different kind of question — not “will it happen” but “what shape is this” — and if that is close enough to what you came for, it is one page away.
Closing note — a page that says 'not built' out loud
To sum up: Liu Yao stacks 納甲, the 世/應 positions, the six relatives and a focus line on top of the same sixty-four hexagrams to answer 'will it happen, and when'. Bokki computes none of that stack — our share ends at the common layer: the sixty-four figures, their texts, and the two casting methods.
This page copies the actual boundary of our repository. Writing down exactly where the engine ends, instead of padding a feature list, is what our rule — claiming to compute what you do not compute is the end of you — looks like in article form. The day we finish cross-checking the 納甲 tables against multiple editions, this article will be the first thing we rewrite.