A unified approach to construction of Gelfand-Tsetlin-Zhelobenko base vectors for series $A$, $B$, $C$, $D$

Using the Zhelobenko’s approach we investigate a branching of an irreducible representation of $g_n$ under the restriction of algebras $g_n\downarrow g_{n-1}$,where$g_n$isaLiealgebraoftype$B_n$,$C_n$,$D_n$ or a Lie algebra of type $A$, where in this case we put $g_n={\mathfrak{g}\mathfrak{l}}_{n+1}$, $g_{n-1}={\mathfrak{g}\mathfrak{l}}_{n-1}$. We give a new explicit description of the space of the $g_{n-1}$-highest vectors, then we construct a base in this space. The case $n=2$ is considered separately for different algebras, but a passage from $n=2$ to an arbitrary $n$ is the same for all series $A$, $B$, $C$, $D$. This new procedure has the following advantage: it establishes a relation between spaces of $g_{n-1}$-highest vectors for different series of algebras. This procedure describes an extension of Gelfand-Tsetlin tableaux to the left.