A natural geometric construction underlying a class of Lax pairs
  In the framework of the theory of differential coverings \cite{KV}, we discuss a general geometric construction that serves the base for the so-called Lax pairs containing differentiation with respect to the spectral parameter \cite{OS}. Such kind of objects arise, for example, when studying integrability properties of equations like the Gibbons-Tsarev one \cite{GT}. 
Joseph Krasil'shchik
nlin.SI math.DG