EN
We deal with projective limits of classes of functions and prove that: (a) the Chebyshev polynomials constitute an absolute Schauder basis of the nuclear Fréchet spaces $𝓔_{(𝔐)}([-1,1]^r)$; (b) there is no continuous linear extension map from $Λ^{(r)}_{(𝔐)}$ into $𝓑_{(𝔐)}(ℝ^r)$; (c) under some additional assumption on 𝔐, there is an explicit extension map from $𝓔_{(𝔐)}([-1,1]^r)$ into $𝓓_{(𝔐)}([-2,2]^r)$ by use of a modification of the Chebyshev polynomials. These results extend the corresponding ones obtained by Beaugendre in [1] and [2].