bool x,y,z;

x := true;
y := true;
z := x <=> y;
print x,y,z;

x := true;
y := false;
z := x <=> y;
print x,y,z;

x := false;
y := true;
z := x <=> y;
print x,y,z;

x := false;
y := false;
z := x <=> y;
print x,y,z