Orthogonality and characterizations of inner product spaces
O. P. Kapoor, J. Rajendra Prasad · Bulletin of the Australian Mathematical Society · 1978
Using the notions of orthogonality in normed linear spaces such as isosceles, pythagorean, and Birkhoff-James orthogonality, in this paper we provide some new characterizations of inner product spaces besides giving simpler proofs of existing similar characterizations. In addition we prove that in a normed linear space pythagorean orthogonality is unique and that isosceles orthogonality is unique if and only if the space is strictly convex.