Generalized gyrovector spaces and the positive cone of Contact Information: ∗ Faculty of Engineering a unital C -algebra Niigata University 8050 2no-cho ikarashi Nishi-ku Niigata-shi, Niigata- ken, Japan Toshikazu Abe Phone: +81 (25) 262 7469 Niigata University, Faculty of Engineering Email:
[email protected] Abstract Definition 1. A magma (G; ⊕) is called a gyrogroup if there exists an Note that a real normed space (V; +; ×) is a GGV with ϕ = idV. Results The concept of generalized gyrovecor space (GGV, for short) is a com- element e such that the binary operation ⊕ satisfies the following (G1) On a GGV, we can define the gyromidpoint. It is a algebraic mid- mon generalization of the concept of real normed spaces and of the gyrovector spaces. The addition of a GGV is not necessarily a commutative group but is a to (G5). point on the GGV. On a real normed space, the gyromidpoint is the A Mazur-Ulam Theorem for GGV’s gyrocommutative gyrogroup. A typical example of GGV’s is the positive cone 8 2 ⊕ arithmetric mean. ∗ (G1) a G, e a = a. of a unital C -algebra. (G; ⊕; ⊗) p(a; b) We have a Mazur-Ulam type theorem for GGV’s as follows. This is a (G2) 8a 2 G, 9 ⊖ a s.t. ⊖a ⊕ a = e: Definition 4. Let be a GGV. The gyromidpoint of a; b 2 (G; ⊕; ⊗) is defined as p(a; b) = 1 ⊗ (a ⊞ b), where ⊞ is the generalization of the celebrated Mazur-Ulam theorem. A proof of this 8 2 9 2 ⊕ ⊕ ⊕ ⊕ 2 (G3) a; b; c G, ! gyr[a; b]c G s.t.