Then the sequence g(t) will eventually match the position of the spy at a + b t. if log_2 max(1 +|a|, 1+|b|) <= n, then will will find the spy before t = 4^(n+1).

This can be made less redundant by replacing e and f with e' = e – c + 1, f' = f – d + 1 but the analysis would be trickier.

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