Formally self-adjoint quasi-differential operators and boundary value   problems
  We develop the machinery of boundary triplets for one-dimensional operators generated by formally self-adjoint quasi-differential expression of arbitrary order on a finite interval. The technique are then used to describe all maximal dissipative, accumulative and self-adjoint extensions of the associated minimal operator and its generalized resolvents in terms of the boundary conditions. Some specific classes are considered in greater detail. 
Andrii Goriunov, Vladimir Mikhailets, Konstantin Pankrashkin
math.FA