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4h
revised choose from implication and logical and in write assertions in first-order logic
added 25 characters in body
5h
answered choose from implication and logical and in write assertions in first-order logic
Jul
30
comment Prove that a morphism $\alpha$ of $Fun(\mathcal{A},\mathcal{B})$ is an isomorphism iff each component $\alpha_A$, is an isomorphism in $\mathcal{B}$
Drhab's proof is just fine (of course). You'll find much the same argument as the proof for Theorem 21 in these Notes on Basic Category Theory -- which I mention because the Notes spell out lots of elementary proofs in detail, useful if you want to "learn how to make proofs in category theory working with the very basic concepts".
Jul
30
revised Proof outline of a certain sentence (Introductory course on logic, proof writing et al.)
added 17 characters in body
Jul
30
answered Proof outline of a certain sentence (Introductory course on logic, proof writing et al.)
Jul
28
comment Solve the following proof : M |- M ∨ {[(Z∨S) ∧ (¬] → (C↔D)}
Looks like a standard Natural Deduction system in Fitch-style. Or-introduction, $\lor I$ should normally be a basic rule. Check it out.
Jul
28
revised Solve the following proof : M |- M ∨ {[(Z∨S) ∧ (¬] → (C↔D)}
edited body
Jul
28
comment Solve the following proof : M |- M ∨ {[(Z∨S) ∧ (¬] → (C↔D)}
OK, that's what I assumed: so which proof system are you supposed to be using?
Jul
28
answered Solve the following proof : M |- M ∨ {[(Z∨S) ∧ (¬] → (C↔D)}
Jul
28
answered Spot the error in experimenting with contradiction on 5's rationality.
Jul
21
revised A tautology that contains quantifier and logical connective.
added 7 characters in body
Jul
20
revised A tautology that contains quantifier and logical connective.
added 50 characters in body
Jul
20
revised A tautology that contains quantifier and logical connective.
added 358 characters in body
Jul
20
answered A tautology that contains quantifier and logical connective.
Jul
18
revised A proof that right adjoints preserve limits?
added 150 characters in body
Jul
16
answered Easiest way to see that $\mathcal{C}$ is cocomplete?
Jul
14
revised A proof that right adjoints preserve limits?
added 21 characters in body
Jul
14
comment A proof that right adjoints preserve limits?
Sorry, @darijgrinberg -- I realised there was a garble in the way I put things before, so I've slightly edited. And points numbered (1) and (2) have gone. So, for others, (2) is the claim that G preserves limits in the full sense as now defined in the fourth para.
Jul
14
revised A proof that right adjoints preserve limits?
deleted 509 characters in body
Jul
14
comment Is it necessary for a statement to have an inverse in propositional logic?
What do you mean by "inverse"? Is the inverse of a proposition its negation?