$(x+1)^2+(y+1)^2+(x-y)^2=2$
TH1: $\left \{ {{(x+1)^2=0} \atop {(y+1)^2=1}} \atop {(x-y)^2=1} \right.$ ⇒$\left \{ {{x=-1} \atop {y=0;y=-2}} \atop{⇒(x=-1;y=-2);(x=-1;y=0)} \right.$
TH2: $\left \{ {{(y+1)=0} \atop {(x+1)^2=1}} \atop{(x-y)^2=1} \right.$ =>$\left \{ {{y=-1} \atop {x=0;x=-2}} \atop {⇒(x=-1;y=0);(y=-1;x=-2)} \right.$ } \right.$
Th3: $\left \{ {{(x-y)^2=0} \atop {(y+1)^2=1}}\atop{(x+1)^2=1} \right.$ =>$\left \{ {{(x=y=0);(x=y=-2)} \atop {y=0;y=-2}}\atop{x=0;x=-2} \right.$
