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'Level grading' a new graded algebra structure on differential polynomials: application to the classification of scalar evolution equations
(IOP Publishing Ltd, 2013)
We define a new grading which we call the 'level grading' on the algebra of polynomials generated by the derivatives u(k+i) over the ring K-(k) of C-infinity functions of x t u u(1) ... u(k) where . This grading has the ...