Let f be an integer greater than one. We study three progressively finer equivalence relations on closed 3-manifolds generated by Dehn surgery with denominator f : weak f -congruence, f -congruence, and strong f -congruence. If f is odd, weak f -congruence preserves the ring structure on cohomology with ޚ f -coefficients. We show that strong f -congruence coincides with a relation previously studied by Lackenby. Lackenby showed that the quantum S U.2/ invariants are well-behaved under this congruence. We strengthen this result and extend it to the SO.3/ quantum invariants. We also obtain some corresponding results for the coarser equivalence relations, and for quantum invariants associated to more general modular categories. We compare S 3 , the Poincaré homology sphere, the Brieskorn homology sphere †.2; 3; 7/ and their mirror images up to strong f -congruence. We distinguish the weak f -congruence classes of some manifolds with the same ޚ f -cohomology ring structure.
57M99; 57R56