Two (six?) types of efficient markets

This blog post points out the efficient markts hypothesis can either mean that prices are correct, or that there is no free lunch: that it is not possible to beat the market without taking on extra risk. I am not sure that this is a very scientific distinction, because I do not see how to test the difference.

If we do accept that these are the two main variants (I think further subtleties are possible), then, presumably each exists in strong, semi-strong and weak forms (the linked article was updated today to better explain the different variants of EMH), so we have a total of six variants. Test that!

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