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jonathanichikawa / for-all-x

Open-source logic textbook in LaTeX by UBC philosophy professor Jonathan Ichikawa
Creative Commons Attribution 4.0 International
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errors in ch. 7 answer key #5

Closed jonathanichikawa closed 5 years ago

jonathanichikawa commented 5 years ago

Several small errors relating to the justification of ND proofs:

answer key for Ch. 7 B 3, line 6: for consistency, list line numbers in order for the justification (4, 5) B 6, line 10: justification should cite both 4–8 and 4–9 D 2, line 5: justification should be ~E, not ~I. D 3: this is oddly done. The simplest correction would be to change the line 5 justification to ~E instead of ~I. But it would be better to rework this proof so that it assumes P & ~P and uses ~E. D 4, line 8: justification should cite 1–7, not 1–2. D 5, line 2: missing close parenthesis at end of line F 4, line 4: remove two extra close parentheses at end of line

jonathanichikawa commented 5 years ago

I believe I've now correct all of these issues.