Thank you, Zaxo, for that reference.
Following up, I have found: Augustus De Morgan originally observed that in classical propositional logic the following relationships hold:
not (P and Q) = (not P) or (not Q)
not (P or Q) = (not P) and (not Q)
This explains why the following are equivalent instructions: print "no editor found\n"
if ! (defined $ENV{EDITOR} || defined $ENV{VISUAL});
print "no editor found\n"
if (!defined $ENV{EDITOR} && !defined $ENV{VISUAL});
Thank you for setting me straight! This has been very helpful! |