A comparison sets one thing against another at ratio x and costs J(x) = ½(x + 1/x) − 1. At ratio 2, one side twice the other, it costs J(2) = 1/4. Read the other way round, at ratio 1/2, it costs 1/4 again. At ratio 1/100 it costs 49.005. At ratio 1 the two sides are equal, nothing is told apart, and J(1) = 0.
Two conditions leave one cost, J. First, costs combine consistently: J(xy) + J(x/y) = 2J(x)J(y) + 2J(x) + 2J(y). Second, the cost curves at unit rate near ratio one. No other cost meets both; no continuity is assumed beyond the curvature condition. J is zero only at ratio one and passes every bound as one side shrinks toward zero, so no start sits at that limit. A void, where no two things differ, hosts no distinction at all: nothing in it can be told apart, so no first event can change it. The empty record costs exactly zero: nothing has been compared yet. A comparison at ratio 1 keeps the total at zero, since J(1) = 0; every other comparison adds to it. The void can’t even hold two things that differ; the empty record sits in a world that can, before any comparison has been made. Under the premise, the empty books are the start; step 3 shows that no posting law supplies the premise.
Proved.
Standard mathematics
J ≥ 0 is the inequality of arithmetic and geometric means; the law for combining costs is d’Alembert’s functional equation once 1 is added. Unit curvature is a limit condition at ratio one; together with the law it makes the cost zero there and continuous there, and the classical theory of that equation (Aczél, Kannappan) leaves only J. New: a short direct proof that assumes no continuity beyond the curvature condition.
Working paper: Before the First Event: The Empty Record, sections 2 to 5. Paper page: the price of telling two things apart is forced. Essay: Why Is There Something Rather Than Nothing? Published: Uniqueness of the Canonical Reciprocal Cost, Mathematics 14(6), 935 (2026)