`diff'
------

diff(RAT[,VARN]*)

diff(RAT,VARLIST)
     :: RAT $B$r(B VARN $B$"$k$$$O(B VARLIST $B$NCf$NJQ?t$G=g<!HyJ,$9$k(B.

RETURN
     $B<0(B

RAT
     $BM-M}<0(B ($B=iEyH!?t$r4^$s$G$b$h$$(B)

VARN
     $BITDj85(B

VARLIST
     $BITDj85$N%j%9%H(B

   * $BM?$($i$l$?=iEyH!?t$r(B VARN $B$"$k$$$O(B VARLIST $B$NCf$NJQ?t$G(B
     $B=g<!HyJ,$9$k(B.

   * $B:8B&$NITDj85$h$j(B, $B=g$KHyJ,$7$F$$$/(B. $B$D$^$j(B, diff(RAT,x,y) $B$O(B,
     diff(diff(RAT,x),y) $B$HF1$8$G$"$k(B.

     [0] diff((x+2*y)^2,x);
     2*x+4*y
     [1] diff((x+2*y)^2,x,y);
     4
     [2] diff(x/sin(log(x)+1),x);
     (sin(log(x)+1)-cos(log(x)+1))/(sin(log(x)+1)^2)
     [3] diff(sin(x),[x,x,x,x]);
     sin(x)

