Quant Trade — Jane Street Mental Model

The Jane Street meme: trading is applied probability theory at industrial scale. Every position is a bet; every bet is priced by expected value; every edge is measured, monitored, and managed.

The Jane Street Operating System

Five axioms that govern all decisions:

1. EV first — before entering any trade, compute E[P&L]. If EV ≤ 0, don't trade
2. Risk is a cost — wider spread = compensation for inventory risk and adverse selection
3. Condition on fill — when your passive order fills, update your fair value estimate downward (you're probably wrong)
4. Technology + math + domain = edge — no single leg is sufficient alone
5. Porous boundaries — traders, researchers, and engineers share the same goal: find and exploit pricing inefficiencies

Domain Map → Reference Files

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