The interview trading game. Each round I name a quantity; you quote a two-sided market (a bid and an ask) before the clock runs out. Then I trade against you: if the true value is above your ask I lift you (you sold too cheap); if it's below your bid I hit you (you bought too rich); if it lands inside your market you hold and earn the edge — more for a tighter quote. Tight and accurate makes money; lazy-wide makes nothing; wrong gets run over.
With bid B, ask A (so width = A − B), true value V, and a fair width Wf for the question:
A − V (you sold a contract at A that was worth V).V − B (you bought at B something worth V).max(0, Wf − width) — you earn the edge, and the tighter you quoted, the more.−Wf.It is mildly negative-sum, like real two-sided trading against informed flow: you make money by being tight and right, and by widening only when you are genuinely unsure.