Factorize an unit : ufactor

ufactor factorizes an unit in a unit object : the first argument is an unit object and the second argument is the unit to factorize.
The result is an unit object multiplicated by the remaining MKSA units.
Input :

ufactor(3_J,_W)

Output :

3_(W*s)

Input :

ufactor(3_W,_J)

Output :

3_(J/s)