It means the same as "at least as good as". If X is as good as Y, if not better, then X may be better than Y, the speaker is not sure, but in any case X is certainly as good as Y. In mathematical terms, if X is as good as Y, then: goodness of X = goodness of Y If X is better than Y, then: goodness of X > goodness of Y If X is as good as Y, if not better, then: goodness of X = goodness of Y and maybe goodness of X > goodness of Y.
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