In a space equipped with a symmetric,
or Hermitian form, the orthogonal sum is the direct sum of two subspaces and , which are mutually orthogonal. It is denoted .
denotes a direct sum of subspaces of which are pairwise orthogonal.
This entry contributed by Margherita
More things to try:
Barile, Margherita. "Orthogonal Sum." From MathWorld--A Wolfram Web Resource, created by Eric
W. Weisstein. https://mathworld.wolfram.com/OrthogonalSum.html