Here is a onedimensional \"toy" example to illustrate how the Robin boundary con dition (% + aims = 0 could allow a nonunique solution in some cases if we did not insist that the function a should be nonnegative on the boundary S. Suppose we are solving the \"onedimensional Laplace equation" '32:\" = I] on the real line in the interval I] 5 .1: 5 L. {So in this problem, the \"volume\" V is the one-dimensional interval 0