TWO-DISTANCE PRESERVING FUNCTIONS FROM EUCLIDEAN SPACE

Let 0 < c < s be fixed real numbers such that \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $${c \mathord{\left/ {\vphantom {c s}} \right. \kern-\nulldelimiterspace} s} \leqslant {{\left( {\sqrt 5 - 1} \right)} \mathord{\left/ {\vphantom {{\left( {\sqrt 5 - 1} \right)} 2}} \right. \kern-\nulldelimiterspace} 2}$$ \end{document}, and let f : E2 → Ed for d ≥ 2 be a function such that for every p, q ∈ E2 if ¦p − q¦ = c, then ¦f(p) − f(q)¦ ≤ c, and if ¦p − q¦ = s, then ¦f(p) − f(q)¦ ≥ s. Then f is a congruence. This result depends on and expands a result of Rádo et. al. [9], where a similar result holds, but for \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $${{\sqrt 3 } \mathord{\left/ {\vphantom {{\sqrt 3 } 3}} \right. \kern-\nulldelimiterspace} 3}$$ \end{document} replacing \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $${{\left( {\sqrt 5 - 1} \right)} \mathord{\left/ {\vphantom {{\left( {\sqrt 5 - 1} \right)} 2}} \right. \kern-\nulldelimiterspace} 2}$$ \end{document}. We also present a further extensions where E2 is replaced by En for n > 2 and where the range of c/s is enlarged.