System S9 (Hughes and Cresswell)


[Åqvist, 1964] called this system 7.5, but it contains S8 (as pointed out in [Hughes and Cresswell, 1968, p272])

Åqvist really built this as S7.5 (S9) =S3.5+S [MMp], and S3.5 = S3 + 5 [Mp>LMp] [Åqvist, 1964, p82]

This system is 8pc (Pledger) [Pledger, 1972, 277-fn4]

Based on

The system S7.5 (S9) is: S3.5 + MMp [S] [Åqvist, 1964, p82] [Hughes and Cresswell, 1996, p208, p364]


The system S9 is: S3 + Axiom 5[Mp>LMp] + MMp [S] [Hughes and Cresswell, 1996]

H&C really say: s9 = s3.5 + MMp and S3.5 = S3 + 5(E), therefore the above.


The system S9 (8pc) is 8p + either of

[Pledger, 1972, 279]

The system S9 (8pc) is 12r (S3.5) plus any of

[Pledger, 1972, 279]

Basis for

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