Propositional Logic · First-Order Logic (Optional)

Lesson 7

Nikolai Chukhin · Alexander S. Kulikov

Problem. Which of the following formulas is satisfied by the model \(\mathbb{N}\)?

1 point

  1. \(\forall x \ \exists y \ (y < x)\)

  2. \(\exists x \ (x \times x = \sigma(\sigma(0)))\)

  3. \(\forall x \ \forall y \ (x + y = y + x)\)

  4. \(\exists x \ (\sigma(x) \neq \sigma(\sigma(\sigma(0))))\)