EN
Let R be a real closed field, and denote by $𝓔_{R,n}$ the ring of germs, at the origin of Rⁿ, of $C^∞$ functions in a neighborhood of 0 ∈ Rⁿ. For each n ∈ ℕ, we construct a quasianalytic subring $𝓐_{R,n} ⊂ 𝓔_{R,n}$ with some natural properties. We prove that, for each n ∈ ℕ, $𝓐_{R,n}$ is a noetherian ring and if R = ℝ (the field of real numbers), then $𝓐_{ℝ,n} = 𝓗ₙ$, where 𝓗ₙ is the ring of germs, at the origin of ℝⁿ, of real analytic functions. Finally, we prove the Real Nullstellensatz and solve Hilbert's 17th Problem for the ring $𝓐_{R,n}$.