Distinguishes payoff-space no-arbitrage, which follows from terminal payoffs, from protocol-executable no-arbitrage, which depends on what position transformations traders can actually perform. Using Polymarket's negative-risk markets and the NegRisk Adapter, the authors reconstruct depth-aware portfolio values and transaction histories to measure payoff-bound violations: an estimated $1.12 million in arbitrage profit across two realization channels. Violations concentrate on the unsupported YES side, while adapter-supported NO-side violations are rarer and shorter-lived. The takeaway: market efficiency depends not only on payoff structure, but on whether protocols expose payoff equivalences as executable primitives.

Analyzes 23 million moneyline trades on Kalshi across major sport leagues and finds two systematic ways market prices fail as probabilities. Calibration is not static: parameters sit near perfect-calibration values mid-contract but depart sharply as expiry approaches, with the final ten minutes producing a step-like Prelec curve consistent with insurance-demand behavior by traders holding losing positions. Cross-game parlays are systematically overpriced relative to the product of their leg prices, with overpricing growing in leg count and a separate market-level markup at the parlay-pricing stage. The practical takeaway: treating prediction-market prices as probabilities requires conditioning on time to expiry and product type, not just price.