 Laws are always true; while they have the same form as constraints they constrain only vacuously in that every valuation of their variables is a solution. The constraint \(x^2 +y^2 = 1\) has a continuum of solutions forming a shape, in this case a circle of radius 1. The constraint \(2x^2 -x+3 = 5x-1\) has two solutions, \(x = 1\) or 2, and may be encountered in the solution of word problems, or in the determination of the points of intersection of two curves such as the parabola \(y = 2x^2 -x+3\) and the line \(y = 5x-1\).