add

<< obj1 obj2 add obj3 >>
obj3 is the sum of obj1 and obj2.
If obj1=f1/f2, obj2=g1/g2, then obj3 is given by (g2 f1 + f2 g1)/(f2 g2)
Example:  2 3 add ::  ==> 5



Nobuki Takayama 2020-11-24