Okay:

SOTNEW.mw

@Carl Love 

I need set minus before find derivative

I try

temp :=tau-> (-D@@2)(Kx);

temp :=tau-> (D@@2)(-Kx);

temp :=tau-> -(D@@2)(Kx);

but get something like this if print temp

-(tau-> .....) , i want like this tau->-....

If i use temp:=tau->-diff(Kx(tau),tau$2)

then i got

Dy := Ky(0);
Error, (in temp) invalid input: diff received 0, which is not valid for its 2nd argument