PHIL1012 Introductory Logic · Problem Set 6 · Week 10
1. Use a tree to test whether the following argument is valid. (Present the tree, and say whether the argument is valid or invalid.) If the argument is invalid, read off a counterexample from your tree (and indicate the path from which you are reading it off).
∀xCx → ¬∃yDy
Cb ∧ Db
∃z¬Cz
2. Use a tree to test whether the following two propositions are equivalent. (Present the tree, and say whether they’re equivalent or not.) If they’re not equivalent, read off from your tree a model on which the propositions have different truth values (and indicate the path from which you are reading it off).
∀x(Ax → Gx)
∃x(Ax → Gx)