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A fundamental property of all hash functions is that if two hashes (according to the same function) are different, then the two inputs were different in some way. This property is a consequence of hash functions being deterministic, mathematical functions, but they are generally not one-to-one, with a large domain and smaller range. Consequently, the equality of two hash values does not guarantee the two inputs were the same, but in some cases, probability theoretic or computability theoretic guarantees apply.
