Extending the corresponding notion for matrices or bounded linear operators on a Hilbert space, we define a generalized Schur complement for a nonnegative linear operator mapping a linear space into its dual, and we derive some of its properties.
"A generalized Schur complement for nonnegative operators on linear spaces." Banach J. Math. Anal. 12 (3) 617 - 633, July 2018. https://doi.org/10.1215/17358787-2017-0061