Let M be a compact
Hausdorff space. Let 𝒞(M) denote the Banach space of continuous functions f on M.
We are interested in functionals Φ on 𝒞(M) with the following properties: (i)
|Φ(f)|≦∥f∥ for every f ∈𝒞(M), (ii) Φ(f + g) = Φ(f) + Φ(g) whenever
fg = 0, (iii) Φ(f + α) = Φ(f) + α for every f ∈𝒞(M) and every real number
α.