x1 = false;
x2 = false;
x3 = false;
----------
x1 = true;
x2 = false;
x3 = false;
----------
x1 = false;
x2 = true;
x3 = false;
----------
x1 = true;
x2 = true;
x3 = false;
----------
x1 = true;
x2 = false;
x3 = true;
----------
==========