EN
If C is a capacity on a measurable space, we prove that the restriction of the K-functional $K(t,f;L^p(C),L^∞(C))$ to quasicontinuous functions f ∈ QC is equivalent to
$K(t,f;L^p(C) ∩ QC, L^∞(C) ∩ QC)$.
We apply this result to identify the interpolation space $(L^{p₀,q₀}(C) ∩ QC,L^{p₁,q₁}(C) ∩ QC)_{θ,q}$.