Dokl. Akad. Nauk SSSR, 1967 Volume 173, Number 4,Pages 758–761(Mi dan32985)
MATHEMATICS
Unitary extensions of isometric operators in the Pontrjagin space $\Pi_1$ and continuations in the $\mathfrak{P}_1$
class of finite sequences of the class $\mathfrak{P}_{1;n}$