Description: A kind of Aristotelian inference. Proposition 59 of Frege1879 p. 51.
Note: in the Bauer-Meenfelberg translation published in van
Heijenoort's collectionFrom Frege to Goedel, this proof has the
frege12 incorrectly referenced where frege30 is in the original.
(Contributed by RP, 24-Dec-2019)(Proof modification is discouraged.)