See my following testing:
In[199]:= Assuming[{n1,n2,n3}\[Epsilon] Integers, FractionalPart[n1 + 2 n2 - 3 n3 ]]
FullSimplify[FractionalPart[n1 + 2 n2 - 3 n3], {n1,n2,n3}\[Epsilon] Integers ]
Out[199]= FractionalPart[n1 + 2 n2 - 3 n3]
Out[200]= FractionalPart[n1 + 2 n2 - 3 n3]
Why can't I simplify the results, that is, return the correct results 0?
Regards, Zhao