Bryant, R.
Exterior differential systems and Euler-Lagrange partial differential equations - Chicago University of Chicago Press 2003 - vii, 213p. - Chicago lectures in mathematics series .
0-226-07793-4
Exterior differential systems and Euler-Lagrange partial differential equations - Chicago University of Chicago Press 2003 - vii, 213p. - Chicago lectures in mathematics series .
0-226-07793-4