Which one of the following options is CORRECT given three positive integers x, y and z, and a predicate P(x) = eg (x = 1) ∧ ∀ y ((∃ z (x = y * z)) ⇒ (y = x) ∨ (y = 1))
Topic-wise GATE CS PYQs with verified steps
GATE CSE 2011 · Q30
Time
Select one answerSingle correct
Solution
Official answer: A) P(x) being true means that x is a prime number
Propositional and First-Order LogicLet us analyze the components of the given predicate in the domain of positive integers:
$
eg(x = 1)x \neq 1$.
means that is a factor (divisor) of , since there exists a positive integer such that .
The implication asserts that for every positive integer , if divides , then must be either or .
Combining these two parts:
is a positive integer not equal to .
The only positive divisors of are and itself.
This is precisely the definition of a prime number.
Therefore, being true means that is a prime number, which corresponds to option (A) [p1].
Try the question first, then check your work.
Examiner trap
Analyze the condition alongside over positive integers.
This Propositional and First-Order Logic previous year question is Q30 of the GATE CSE 2011 paper. Find more GATE CSE PYQs on Propositional and First-Order Logic in Engineering Mathematics, or browse all GATE CSE PYQs.
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Propositional and First-Order Logic has 18 GATE CSE PYQs across 16 papers from 2011 to 2026. 7 of them are 2-mark MCQs like this one, and it is the only one in GATE CSE 2011.
How GATE tests Propositional and First-Order LogicIndependent practice explanation verified by the GateAI team. GATE is conducted by the IITs; question text follows the official paper.