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);