>>60
なんか変な変形してるな

dx/dt = 2pt
dt/dx = 1/(2pt)
(d/dx) = (dt/dx)(d/dt) = {1/(2pt)} (d/dt)

{(d/dx)^2} y = ({1/(2pt)} (d/dt)){1/(2pt)} (dy/dt)
= {1/(2pt)} {-1/(2pt^2)} (dy/dt) + {1/(2pt)^2} (d/dt)^2 y

dy/dt = 2p
(d/dt)^2 y = 0