http://dswarmsikhttkg7jgsoyfiqpj3ighupfrvuz5ri3lu5q2dlqyrpgk7ad.onion/notes/lsg.html
Sequent 13.16. modus ponens 13.17. modus tollens 13.18. normal form (Daniel P. Friedman, David Thrane Christiansen, 2018, p. 13) 13.19. canonical expression (Daniel P. Friedman, David Thrane Christiansen, 2018, p. 22) 13.20. constructor 13.21. Gentzen style proof 13.22.