Suppose that the domain of the propositional function P (x) consists of the integers 1, 2, 3, 4, and 5. Express these statements without using quantifiers, instead using only negations, disjunctions, and conjunctions.
e) ∀x((x ≠ 3) → P (x)) ∨ ∃x¬P (x)
but i have a confused that
if x is 3 then (x ≠ 3) is false which means F→ P (x),whatever P(3) is true or false,the statment ∀x((3 ≠ 3) → P (3)) will also be true.Therefore,P(3) is included
if x is 1,2,4,5,then (x ≠ 3) is true which means T→ P (1), T→ P (2),T→ P (4),T→ P (5) is true.
∃x¬P (x) will be (¬P(1)∨¬P(2)∨¬P(3)∨¬P(4)∨¬P(5)).
so the final answer will be (P(1)∧P(2)∧P(3)∧P(4)∧P(5))∨(¬P(1)∨¬P(2)∨¬P(3)∨¬P(4)∨¬P(5)).
However,the actual answer is (P(1)∧P(2)∧P(4)∧P(5))∨(¬P(1)∨¬P(2)∨¬P(3)∨¬P(4)∨¬P(5)).
No, you must include all the evaluations of $P$ that make the conditional true; that means that $(P(3)\vee\neg P(3))$ is included in the leftmost conjunction. Which is a tautology so...