Finding all integral solutions of $x^4+y^4+z^4-w^4=1995$ Find all the integral solutions of 
$$x^4+y^4+z^4-w^4=1995.$$
Please elaborate the solution. I tried but can't understand what to do.

I just figured out that 1995 is a multiple of 5 and by fermat's theorem N^(5-1)=1 mod 5 thus 
LHS x^4+y^4+z^4-w^r=1+1+1-1=3 mod 5
However RHS is 0 mod 5 thus this is not possible 
So now one condition is left when x, y, z, w are multiples of 5
Thus then 
LHS will have 5^4 as its factor which will not completely divide 1995 thus this we will have no solution in integer
