Contradictory propositions in propositional logic remain contradictory in predicate logic due to the extension of formal semantics, making this a matter of fundamental logical definition that requires no external citation.
The claim is a standard deductive truth within formal logic: predicate logic is an extension of propositional logic, and structural contradictions (such as $P ext{ and } eg P$, or universally quantified equivalents) preserve their truth-functional incompatibility. Therefore, this is common knowledge in the context of logic and mathematics, and none of the retrieved applied computer science or linguistic papers directly test or bear on this foundational theorem.