The space of ANR’s in $ℝ^n$
Tadeusz Antoni Dobrowolski, Leonard R. Rubin · Fundamenta Mathematicae · 1994
The hyperspaces $ANR(ℝ^n)$ and $AR(ℝ^n)$ in $2^{ℝ^n} (n ≥ 3)$ consisting respectively of all compact absolute neighborhood retracts and all compact absolute retracts are studied. It is shown that both have the Borel type of absolute $G_{δσ δ}$-spaces and