Selfadjoint Extensions of a Singular Multipoint Differential Operator for First Order

In this work, firstly in the direct sum of Hilbert spaces of vector-functions L^2 (H,(-{\infty},a_1)){\Box}L^2 (H,(a_2,b_2)){\Box}L^2 (H,(a_3,+{\infty})),- {\infty}<a_1<a_2<b_2<a_3<+{\infty} all selfadjoint extensions of the minimal operator generated by linear singular multipoint symmetric differential expression l=(l_1,l_2,l_3),l_k=i d/dt+A_k with a selfadjoint operator coefficient A_k k=1,2,3 in any Hilbert space H, are described in terms of boundary values. Later structure of the spectrum of these extensions is investigated.