Addendum To: The Relationship Between Strong Belief and Assumption (Adam Brandenburger and H. Jerome Keisler)
Synthese, 2023, 201, 175

Proposition 4.1(ii) in the paper is wrong. Example 3.1 in Byung Soo Lee’s “Equivalent Conditional Probability Systems” provides a counter-example. The mistake in our “proof” was that it was a non-proof: It was an assertion of what must be true instead of showing something. I get annoyed with such arguments when I see them in other papers and I am sorry that I too fell into that trap. (Of course, adding details to proofs increases the length of papers. That is not why we made this error—-that was our fault entirely: Just pointing it out as “food for thought.”)