Almost regularity conditions of spectral problems for a second order   equation
  In this paper the asymptotic distributions are exactly solved for linearly independent solutions considering problems of the second order and for the coefficients of asymptotic destribution the recurent formulas are obtained. Further, using obtained recurent formulas the neccessary and sufficient conditions almost regularity of spectral problem for the equation of the second order is proved. 
Yu.A.Mamedov and H.I.Ahmadov