step
fun step(rating: Int, opponentRating: Int, won: Boolean, k: Double = DEFAULT_K, floor: Int = 0, ceiling: Int = 4000): Int
One ELO step. Returns the NEW rating after a bout vs opponentRating, where won is the actual result. The change is k * (actual - expected), rounded so a win moves at least +1 and a loss at least -1 — STRICTLY monotonic in the result regardless of rounding — then clamped to [floor, ceiling].