algebraic relations
X1*X3 + X2*X4 + X1 + X3 + X4
X2*X3 + X1*X4 + X3*X4 + X1 + X2 + X4
X2*X4 + X3*X4 + X1 + X3 + 1
X1*X2 + X1*X3 + X2*X3 + X3 + X4 + 1
X1*X2 + X2*X3 + X1*X4 + X3
X1*X3 + X1*X4 + X3*X4 + X1 + X2 + X3 + X4
X1*X2 + X2*X4 + X1 + 1
end