# evaluate( ds(sin(x)) )=d(sin(x))=cos(x); evaluate(ds(y_)):=d(y); evaluate(ds(y_,x_)):=d(y,x); evaluate(ds(y_,x_,a_)):=d(y,x,a); evaluate(ds(y_,x_,a_,b_)):=d(y,x,a,b); evaluate(log(n_,x_)):=if(abs(n)<=1,(log(x)+psi(1)-psi(1-n))/gamma(1-n)/x^n );