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Quantitative Finance · Glossaire

Qu'est-ce que « Strategy-stealing argument » ?

Definition 12.5 The Interview Book · Chapitre 12 — Brainteasers and Logic

A strategy-stealing argument proves that the first player in a finite game with no draws has a winning strategy, without finding it: if the second player had one, the first player could make an arbitrary move and then follow that strategy as if second, and an extra move never hurts, which is a contradiction.

Exemples

Example 12.6 (A block of trades summing to a multiple of ten)

Among any ten integer P&Ls in sequence, some block of consecutive ones sums to a multiple of ten. The eleven prefix sums (including the empty one) fall into ten residues modulo ten, so two coincide, and the block between them sums to a multiple of ten.

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