M. McIver 1996 An example of non-uniqueness in the two-dimensional water wave problem. Journal of Fluid Mechanics, 315, 257-266.
This is a very significant paper, proving that the two-dimensional water wave problem is not unique. The proof relied on constructing a counter example by producing a wave-free potential which had streamlines which bounded the sigularities. This paper is the starting point for the construction of Trapped Modes.