Gunther's formalism (k-symplectic formalism) in classical field theory:   Skinner-Rusk approach and the evolution operator
  The first aim of this paper is to extend the Skinner-Rusk formalism on classical mechanics for first-order field theories.   The second is to generalize the definition and properties of the evolution K-operator on classical mechanics for first-order field theories using in both cases Gunther's formalism (k-symplectic formalism). 
Angel M. Rey, Narciso Rom\'an-Roy, Modesto Salgado