Question

Fitch proof exercise: showing $(\lnot \forall x \; P(x)) \leftrightarrow (\exists x \lnot P(x))$

score 452 · Answer 1 · 2019-01-05 12:17:40

452

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Fitch proof exercise: showing $(\lnot \forall x \; P(x)) \leftrightarrow (\exists x \lnot P(x))$

Published on 05 Jan 2019 - 12:17

score 306 · Answer 2 · 2026-03-25 05:59:57

306

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Proof using natural deduction (Tautology)

Published on 25 Mar 2026 - 5:59

score 91 · Answer 3 · 2026-03-26 06:28:22

91

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Prove that there is a $\Delta_1$-set $E$ which satisfies $S_0 \setminus S_1 \subset E \subset S_0$

Published on 26 Mar 2026 - 6:28

score 61 · Answer 4 · 2026-03-26 06:28:40

61

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Prove that image and preimage of $\Sigma_1$-sets under a function with a $\Sigma_1$-graph are $\Sigma_1$-sets

Published on 26 Mar 2026 - 6:28

score 61 · Answer 5 · 2019-01-08 12:47:49

61

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Logical equivalence versus definitional equality

Published on 08 Jan 2019 - 12:47

score 77 · Answer 6 · 2019-01-08 21:41:51

77

Views

Extension of a theory

Published on 08 Jan 2019 - 21:41

score 165 · Answer 7 · 2019-01-09 15:16:55

165

Views

Clarification on set definitions from How to Prove it (Velleman) Chapter 2.3

Published on 09 Jan 2019 - 15:16

score 61 · Answer 8 · 2026-03-25 04:35:16

61

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Translate a sentence into predicate logic

Published on 25 Mar 2026 - 4:35

score 67 · Answer 9 · 2019-01-13 03:45:56

67

Views

logic contradiction

Published on 13 Jan 2019 - 3:45

score 117 · Answer 10 · 2026-03-26 11:16:45

117

Views

Is there a notation for the unique value that satisfies a predicate?

Published on 26 Mar 2026 - 11:16

score 121 · Answer 11 · 2019-01-14 15:16:46

121

Views

Distinguish 'the only f are g' from 'only f are g' in predicate logic

Published on 14 Jan 2019 - 15:16

score 64 · Answer 12 · 2019-01-15 01:39:02

64

Views

How to write this $(\exists (x,y) \in R, y- 3x-2 \wedge y = 1-x^2) $in words?

Published on 15 Jan 2019 - 1:39

score 51 · Answer 13 · 2026-03-26 13:51:33

51

Views

Fixing and pointwise-fixing of a structure in a suqare

Published on 26 Mar 2026 - 13:51

score 2.1k · Answer 14 · 2026-03-25 04:41:40

2.1k

Views

Express Negation in Simple English: There is a student in this class who has chatted with exactly one other student

Published on 25 Mar 2026 - 4:41

score 102 · Answer 15 · 2019-01-17 16:20:30

102

Views

How to prove (4|n)→(2|n) in P

Published on 17 Jan 2019 - 16:20

List Question

Fitch proof exercise: showing $(\lnot \forall x \; P(x)) \leftrightarrow (\exists x \lnot P(x))$

Proof using natural deduction (Tautology)

Prove that there is a $\Delta_1$-set $E$ which satisfies $S_0 \setminus S_1 \subset E \subset S_0$

Prove that image and preimage of $\Sigma_1$-sets under a function with a $\Sigma_1$-graph are $\Sigma_1$-sets

Logical equivalence versus definitional equality

Extension of a theory

Clarification on set definitions from How to Prove it (Velleman) Chapter 2.3

Translate a sentence into predicate logic

logic contradiction

Is there a notation for the unique value that satisfies a predicate?

Distinguish 'the only f are g' from 'only f are g' in predicate logic

How to write this $(\exists (x,y) \in R, y- 3x-2 \wedge y = 1-x^2) $in words?

Fixing and pointwise-fixing of a structure in a suqare

Express Negation in Simple English: There is a student in this class who has chatted with exactly one other student

How to prove (4|n)→(2|n) in P

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