  Using a (1,1)-tensor L with zero Nijenhuis torsion and maximal possible
number (equal to the number of dependent variables) of distinct, functionally
independent eigenvalues we define, in a coordinate-free fashion, the seed
systems which are weakly nonlinear semi-Hamiltonian systems of a special form,
and an infinite set of conservation laws for the seed systems.
  The reciprocal transformations constructed from these conservation laws yield
a considerably larger class of hydrodynamic-type systems from the seed systems,
and we show that these new systems are again defined in a coordinate-free
manner, using the tensor L alone, and, moreover, are weakly nonlinear and
semi-Hamiltonian, so their general solution can be obtained by means of the
generalized hodograph method of Tsarev.
