GCD _ _ _ _ _ _ _ _ _ _ _ _ switch

When gcd is on, common factors in numerators and denominators of expressions are canceled. Default is off.

examples:

(2*(f*h)**2 - f**2*g*h - (f*g)**2 - f*h**3 + f*h*g**2
   - h**4 + g*h**3)/(f**2*h - f**2*g - f*h**2 + 2*f*g*h
   - f*g**2 - g*h**2 + g**2*h);
 

   2  2    2          2  2      2        3      3    4
  F *G  + F *G*H - 2*F *H  - F*G *H + F*H  - G*H  + H
  ---------------------------------------------------- 
    2      2        2                2    2        2
   F *G - F *H + F*G  - 2*F*G*H + F*H  - G *H + G*H


on gcd; 

ws; 

                 2
  F*G + 2*F*H + H
  ---------------- 
       F + G


e2 := a*c + a*d + b*c + b*d; 

  E2 := A*C + A*D + B*C + B*D 


off exp; 

e2; 

  (A + B)*(C + D)

Even with gcd off, a check is automatically made for comm on variable and numerical products in the numerators and denominators of expression, and the appropriate cancellations made. Thus the example demonstrating the use of gcd is somewhat complicated. Note when exp is off, gcd has the side effect of factoring the expression.