defrule or similar



I have a problem for a long time. I am trying to avoid the expansion
of term like 

sin(A+B)+sin(A-B)

I know that my results will be functions of sin(A+B+C+...) and
cos(A+B+C+...) etc...  but in the middle of the generation process
appear lots of terms like

sin(A+B)+sin(A-B)
sin(A+B+C)+sin(A+B-C)

so one alternative is to avoid that these term grow. However I could
not do this up to now.

Any help will be very important.

Daniel




(C4) matchdeclare([A,B],true);

(D4) 				     DONE

(... lots of trials ...  and again to the beginning )

(C122) defrule(cAB2,sin(A+B)+sin(A-B),2*sin(A)*cos(B));

B + A partitions SUM
(D122) 	       cAB2 : SIN(B + A) - SIN(B - A) -> 2 SIN(A) COS(B)
(C123) HH:SIN(Y + X) - SIN(Y - X);

(D123) 			    SIN(Y + X) - SIN(Y - X)
(C124)