User:Msrasnw/testmaths

$f(\mathbf {x} +{\frac {\mathbf {p} }{m}}\,dt,\mathbf {p} +\mathbf {F} \,dt,t+dt)\,d\mathbf {x} \,d\mathbf {p} =f(\mathbf {x} ,\mathbf {p} ,t)\,d\mathbf {x} \,d\mathbf {p} ,$