By the recursion operator of the Kaup-Newell hierarchy we construct the
relativistic derivative NLS (RDNLS) equation and the corresponding Lax pair. In
the nonrelativistic limit c→∞ it reduces to DNLS equation
and preserves integrability at any order of relativistic corrections. The
compact explicit representation of the linear problem for this equation becomes
possible due to notions of the q-calculus with two bases, one of which is the
recursion operator, and another one is the spectral parameter
