The Helmholtz conditions for systems of second order homogeneous differential equations
2013 ◽
Vol 83
(1-2)
◽
pp. 71-84
◽
1988 ◽
Vol 8
(3)
◽
pp. 239-248
◽
2007 ◽
Vol 6
(3)
◽
pp. 199-216
◽
2011 ◽
Vol 57
(2)
◽
pp. 409-416
1959 ◽
Vol 7
(3)
◽
pp. 306-310
◽
2015 ◽
Vol 36
(7)
◽
pp. 930-941
1995 ◽
Vol 22
(1)
◽
pp. 45-53
◽