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Sebastian_Hagen2 comments on The Cartoon Guide to Löb's Theorem - Less Wrong

12 Post author: Eliezer_Yudkowsky 17 August 2008 08:35PM

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Comment author: Sebastian_Hagen2 18 August 2008 03:40:40PM 3 points [-]

Doug S.:

What character is ◻?

That's u+25FB ('WHITE MEDIUM SQUARE').

Eliezer Yudkowsky:

Larry, interpret the smiley face as saying:

PA + (◻C -> C) |-

I'm still struggling to completely understand this. Are you also changing the meaning of ◻ from 'derivable from PA' to 'derivable from PA + (◻C -> C)'? If so, are you additionally changing L to use provability in PA + (◻C -> C) instead of provability in PA?