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math.FA2026
On the Fischer-Muszély equation for the positive cones of -algebras
Daisuke Hirota, Jyamira Oppekepenguin
We study the Fischer-Muszély functional equation for the positive semidefinite and the positive definite cones of unital -algebras. We show that any bijection between the posi…
math.FA2026
Surjective isometries on the positive parts of the unit spheres of some function spaces
Yuta Enami, Daisuke Hirota, Hironao Koshimizu +1
We consider the space of continuously differentiable functions on the closed unit interval and the space of Lipschitz continuous fun…
math.FA2026
Globalization of local sign structures for phase-isometries on uniform algebras
Yuta Enami, Daisuke Hirota, Izuho Matsuzaki +1
We study surjective phase-isometries between the unit spheres of uniform algebras. Although such maps preserve maximal convex sets up to signs, the resulting local sign ambiguity p…