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De Morgan's Laws
Disjunctive Laws
Proposition:
Disjunction is
commutative
: for all formulas
A
and
B
A
\/
B
iff
B
\/
A
.
Disjunction is
associative
: for all formulas
A
,
B
, and
C
, we have
A
\/ (
B
\/
C
) iff (
A
\/
B
) \/
C
.
Proof:
by truth tables.
Author:
Wolfgang Schreiner
Last Modification: October 6, 1999