Start squaring

As per given equation on L.H.S. :-

$\sqrt{x-1}-\sqrt{1-x}$

for $\sqrt{x-1}$ and $\sqrt{1-x}$ to be defined , the only permissible value of x is 1.

i.e. DOMAIN of $\sqrt{x-1}-\sqrt{1-x}$ is {1}.

Putting x=1 in the given equation , we get y=-1

so $x-y=1-(-1)=\boxed{2}$

Only $x = 1$ , and $y = -1$ satisfies because $\sqrt { 1 - 1 } - \sqrt { 1 - 1 } = ( 1 - 1 ) ^ { 2 } \Rightarrow \sqrt { 0 } - \sqrt { 0 } = 0 ^ { 2 } \Rightarrow 0 - 0 = 0$ .

So the answer is $1 - ( -1 ) = \boxed { \boxed { \boxed { \boxed { \boxed { 2 } } } } }$ .