B. T. Batikyan
Point derivations on algebraic extension of Banach algebra
(Lobachevskii Journal of Mathematics,
Vol.6, pp.33-37)
It is shown that a point $y_0$ in the carrier space of algebraic
extension $B$
of commutative Banach algebra $A$ is a branch point if and only if
there exists
a local point derivation on $B$ at $y_0$, whose kernel contains $A$.