contrapositive and contradiction
17073
Using proof by contradiction vs proof of the contrapositive
139374
Are these double negatives? "No it is not. No I don't think so."
135957
Why in an inconsistent axiom system every statement is true? (For Dummies)
45380
Surjectivity implies injectivity and conversely
106342
Why $L$-structures cannot satisfy a contradiction
96203
How does negation affect the use and understanding of "or" and "and"
39189
Argue by contradiction to show that there is no surjection...
136577
In formal logic, how is it possible for an argument with a contradictory conclusion to be valid?
52322
Implication in mathematics - How can A imply B when A is False?
136584
Understanding connection between terms tautology, contradiction, contingent, satisfiable, unsatisfiable, valid and invalid
105303
'Obvious' theorems that are actually false
65723
both or either in negative sentences?
10255
Paradoxes without self-reference?
37196
"If P, then Q; If P, then R; Therefore: If Q, then R." Fallacy and Transitivity
49414
Negation in English
115560
Exclusion in formation of comparative statements
5574
Conjectures that have been disproved with extremely large counterexamples?