Corvinta runs two markets on the same pair of dice: A settles at their sum and B at the first die minus the second. Another player quotes A at 6.5 bid, 7.5 offer and B at -0.5 bid, 0.5 offer. The first die is revealed as 5. Update both fair values and find the trades.

With the first die at 5, A is worth 5 + 3.5 = 8.5 and B is worth 5 - 3.5 = 1.5; both offers are stale by 1.0, so lift A at 7.5 and lift B at 0.5. Together the two contracts pay (5 + D2) + (5 - D2) = 10 whatever the second die shows, and you paid 8.0, so the pair locks in 2.0 with no risk. Each leg alone carries a standard deviation of 1.71 for an edge of 1.0; the package carries none.

Before the roll, A is the sum of two dice, mean 7 with a standard deviation of 2.42, and B is their difference, mean 0 with the same spread. The other player's quotes, 6.5 to 7.5 and -0.5 to 0.5, sit around those means. Once the first die shows 5, the only uncertainty left is the second die, with mean 3.5, so A = 5 + D2 is worth 8.5 and B = 5 - D2 is worth 1.5. Both have moved up by 1.5, and both are now uniform over six outcomes, A from 6 to 11 and B from -1 to 4, with a standard deviation of 1.71. The quotes are stale on both: A's offer at 7.5 is a full 1.0 below fair, and B's offer at 0.5 is also 1.0 below fair.

Buying a shop's morning stock and its evening stock separately is two bets on the weather; buying both is a bet on the shop. Contract A is long the second die and contract B is short it, so holding both cancels the second die completely: the package pays 10 with certainty, you paid 8.0, and 2.0 is locked in before the second die is rolled. Each leg on its own has an edge of 1.0 against a standard deviation of 1.71, a fine trade but a coin-flip-sized one; the pair has an edge of 2.0 and no variance, so you take the maximum size the other player allows. The table runs through every value of the second die to show the arithmetic never changes.

Read the two markets together before the roll and they already contain a claim. Since A + B = 2 D1, the two quotes together say twice the first die is worth between 6.0 and 8.0, that is, the first die is between 3 and 4. Any revealed value of 1, 2, 5 or 6, four faces in six, puts the package outside that band and hands you a lock: with a 5 or 6 you lift both offers, with a 1 or 2 you hit both bids. A first die of 2, for instance, makes A worth 5.5 and B worth -1.5; hitting both bids collects 6.0 for a package that will cost you 2 x 2 = 4 to settle, the same lock of 2.0. A quote that is one point wide on a contract with a standard deviation of 2.4 was too tight to begin with; leaving it standing through a reveal is the real error, and it is the one you are being tested on spotting from the other side. The limitation: the lock assumes both trades fill at the quoted size; if the other player pulls one quote after you lift the first, you hold a single leg with edge 1.0 and a standard deviation of 1.71, so lift the leg with the larger size first.