Hintikka on Descartes's Cogito

In the early Sixties Jaakko Hintikka wrote a couple of papers devoted to arguing that Descartes's saying 'cogito ergo sum' is not, contrary to well-established opinion, a deductive inference built upon contingent facts of the matter, but rather a necessarily self-verifying statement of existence. The paper purports to show that, even when read according to Hintikka's interpretation, 'cogito ergo sum' admits of a counterexample, and thus accomplishes much less than it is commonly taken to do by foundationalist programmes in epistemology.