Wigner coefficient for Lie algebras of series $B,C,D$ and a base of Gelfand-Tsetlin type

Abstract: For the Lie algebras $g_n= \mathfrak{o}{2n+1},\mathfrak{sp}{2n},\mathfrak{o}{2n}$ a simple construction of a base in an irreducible representation is given. The construction of this base uses the method of $Z$-invariants of Zhelobenko and the technique of Wigner coefficients, which was applied by Biedenharn and Baird to the construction of a Gelfand-Tsetlin base in the case $\mathfrak{gl}_n$. A relation between matrix elements and Wigner coefficients for $g_n$ and analogous objects for $\mathfrak{gl}{n+1}$ is established.