ExpressionContext.getInstance().addExpression(new Equality(Numbers.variable("x", 1), x1));
ExpressionContext.getInstance().addExpression(new Equality(Numbers.variable("x", 2), x2));
x1 = x1.evaluate();
x2 = x2.evaluate();
ExpressionContext.getInstance().addExpression(new Equality(Numbers.variable("x", 1), x1));
ExpressionContext.getInstance().addExpression(new Equality(Numbers.variable("x", 2), x2));
return new FiniteSet(x1, x2);