Let R be a commutative Noetherian local ring of prime characteristic p and f:R⟶R the Frobenius ring homomorphism. For e≥1 let R(e) denote the ring R viewed as an R -module via fe. Results of Peskine, Szpiro, and Herzog state that for finitely generated modules M, M has finite projective dimension if and only if for all i>0 and all (equivalently, infinitely many) e≥1. We prove this statement holds for arbitrary modules using the theory of flat covers and minimal flat resolutions.
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