load("rncomb")$
/*  COMBINE will not combine the terms in EXP1 because
      their denominators are not identical:   */
EXP1:X/(2*(X+Y))+Z/(X+Y);
COMBINE(EXP1);
/*  RNCOMBINE will: */
RNCOMBINE(%);
/*  RNCOMBINE will combine terms whenever their denominators are
    identical or differ by a numerical factor.  */
EXP2:A/2+B/2+C/3+D/3;
COMBINE(exp2);
RNCOMBINE(exp2);