Joseph B. Keller 
Derivation of the Bohr-Sommerfeld Quantum, Conditions From an Asymptotic Solution, of the Schroedinger Equation [PDF ebook] 

Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. We wish to examine the asymptotic behavior of the of (1) as Planck’s constant h approaches zero. To this end we assume that as h approaches zero.