حمید خدائی

We show that mappings preserving unit distance are close to two-isometries. We also prove that a mapping f is a linear isometry up to translation when f is a two-expansive surjective mapping preserving unit distance. Then we apply these results to consider two-isometries between normed spaces, strictly convex normed spaces and unital C-algebras. Finally, we propose some remarks and problems about generalized two- isometries on Banach spaces.