Polynômes de degré minimum connectant deux projections dans une algèbre de Banach. (Polynomials of minimal degree connecting two projections in a Banach algebra)
Two similar idempotents in a Banach algebra, whose difference is invertible, can be connected within the set of idempotents by a polynomial of degree at most 3. For matrix algebras the assumption on the difference can be dropped.
scientific article; zbMATH DE number 4000760