We extend the Gromov geometric definition of CAT(0) spaces to the case where the comparison triangles are not in the Euclidean plane but belong to a general Banach space. In particular, we study the case where the Banach space is $\ell_p$, for $p > 2$.
"Generalized CAT(0) spaces." Bull. Belg. Math. Soc. Simon Stevin 24 (3) 417 - 426, september 2017. https://doi.org/10.36045/bbms/1506477690