Ideal correspondence for quotients: Let RR be a ring and let I⊲RI\lhd R be a two-sided ideal, with quotient map π:R→R/I\pi:R\to R/I. The assignment

J⟼J/IJ\longmapsto J/I

is a bijection between two-sided ideals J⊲RJ\lhd R with I⊆JI\subseteq J and two-sided ideals of R/IR/I, with inverse K↦π−1(K)K\mapsto \pi^{-1}(K). This correspondence preserves inclusion and carries sums and intersections to sums and intersections.

Remarks

This is the ring form of the applied to the canonical π\pi, and it explains how in a lift and descend. In particular, and of R/IR/I correspond to those of RR that contain II (in the commutative setting).