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1. If the update set contains the reserve currency and it rate isn't 1, the update is rejected.
2. If any new rate falls outside the range [10^{-6}, 10^6]; update is rejected.
3. If any new rate falls outside the range OldRate/2, 2 x OldRate; update is rejected.If any new rate falls outside the range OldRate/
4. if all new rates fall within a multiple of 1.0001 , 1.0001 x OldRate; update of old rates, then the update is accepted but not performed.

If the above validation checks all pass, then exchange rates are updated and rate-dependent cached values are recomputed.

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