What is Liu Yao (六爻)?
The same sixty-four figures, asked a different question — and the East Asian method Bokki has not built.
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”.
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.
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 everything that makes Liu Yao itself. There is no 납갑 stem-and-branch table for the eight trigrams, no eight-palace arrangement to place 세응, no 육친 derivation, no 용신 selection and no timing rule. Each of those is a table we would have to source and cross-check across editions before we trusted it, and we have not done that work.
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.
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.