The stability of certain sets of multiplicity is studied with reference to special classes of differentiable functions. Kronecker sets are produced as examples of instability. The most difficult ...

Let X be a normed linear space, Un an n-dimensional Chebyshev subspace of X. For f ∈ X denote by p(f) ∈ Un its best approximation in Un. The problem of strong unicity consists in estimating how fast ...