3 thoughts on “A triple turnstile!”

  1. Speaking about turnstiles, I wonder if you know who first invented the double turnstile as a symbol for semantic consequence and the model relation? The first appearance known to me is in fact Mendelsons Introduction to Mathematical Logic from 1964 (assuming that it was there already in the first edition, I have access only to the fourth). I tried to investigate this a bit, but found nothing on this matter so far.

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