Triple EMA — 3 * (ema1 - ema2) + ema3, which cancels the lag of a linear trend exactly rather than merely reducing it.

Three chained EMAs, each running over a series that is already na for its own warmup, so the first printed bar is 3 * length - 3 and not length - 1 — see emaOfGapped. close is hard-coded in the reference, so there is no source setting.