Peculiarities of inclined force action upon one-dimensional homogeneous   elastic lumped line
  Exact analytic solutions for one-dimensional elastic lumped line under affection of external force inclined to the axe of line is analyzed. It is shown that in this case an inclined wave being described by implicit function propagates along the line. The conclusions were extended both to unforced vibrations in the line and to distributed-parameters line vibrations. Solution in the form of implicit function is proved as a generalizing one for the wave equation 
Sergey B. Karavashkin (Special Laboratory for Fundamental Elaboration   SELF)