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We show for arbitrary formula `A`

(~by showing (contraposition)forallx:A) => (existsx: ~A)

(~i.e. (propositional consequence and substitution, see next subsection)existsx: ~A) => (~~forallx:A)

(~We assume (*) ~existsx: ~A) => (forallx:A).

Author: Wolfgang Schreiner

Last Modification: November 30, 1999