MAYBE

Problem:
 D(t()) -> 1()
 D(constant()) -> 0()
 D(+(x,y)) -> +(D(x),D(y))
 D(*(x,y)) -> +(*(y,D(x)),*(x,D(y)))
 D(-(x,y)) -> -(D(x),D(y))
 D(minus(x)) -> minus(D(x))
 D(div(x,y)) -> -(div(D(x),y),div(*(x,D(y)),pow(y,2())))
 D(ln(x)) -> div(D(x),x)
 D(pow(x,y)) -> +(*(*(y,pow(x,-(y,1()))),D(x)),*(*(pow(x,y),ln(x)),D(y)))

Proof:
 Open