How to formally prove the negation of a statement "A if and only if B"?
65511
Proving the following false: $f(x)=2x+1$ produces a prime number if and only if x is prime
144396
fitch style proof problem regarding rule of inferences
140634
Double negation and litotes
37369
How do I check if two logical expressions are equivalent?
63854
How do boolean operators work in 'if' conditions?
75381
How can we reason about "if P then Q" or "P only if Q" statements in propositional logic?
62160
Conditional Statements: "only if"
93557
Intuitively, why does (B → S) ≡ (¬B ∨ S)?
132971
Prove that $|a| < b \iff -b<a<b$
80255
How to prove that $|a-b|<\epsilon$ implies $|b|-\epsilon<|a|<|b|+\epsilon$?
50804
It seems obvious, but how to prove it formally?
139600
Bitwise negation gives unexpected result
123458
Prove $( \lnot C \implies \lnot B) \implies (B \implies C)$ without the Deduction Theorem
142026
Show that $A∩B∩C= ∅$ is only true when $A∩B = ∅, A∩C = ∅$ or $B∩C = ∅$ or show a counterexample.
157625
How to prove conditional in Coq?
87928
Proof of logical equivalence of biconditional and other proposition
147947
Does double negation distribute over implication intuitionistically?