Hence the typical Lagrange's equation may be now written in the form

d /dP[Tau]\ dP[Tau] dPV

-- ( ------- ) - ------- = - -----, (13)

dt \dPq`_r / dPq_r dPq_r

or, again,

dP

p`_r = - ----- (V - [Tau]) (14)

dPq_r

It has been proposed by Helmholtz to give the name _kinetic potential_

to the combination V - [Tau].