> > Portia explained to the suitor that of the three statements, at most one was true.
> Notice that the problem condition gives the suitor a certification about the truth of the labels, on which he may rely.
(the first sentence is quoted, approvingly, from a puzzle by Gardner, and the second explains why it saves that puzzle). Sure, there is a certificate provided in the problem; but why may we trust Portia's certification, any more than we may trust the labels on the boxes? It seems that one needs either
- an annoying intra-textual infinite regress: "Portia said this, and Balthazar said that Portia was telling the truth, and Stephano said that Balthazar was telling the truth, …" (which still doesn't really address the trust problem, just moves it infinitely far); or
- a meta-textual reassurance: "Given that at most one of the three statements is true, which of the caskets should the suitor choose?"
(EDIT: Oops, mdpopescu (https://news.ycombinator.com/item?id=9837257) made this point much more succinctly several hours ago.)