“…Free-boundary problems constitute a very active and fast-growing area of research, and a complete, or even thorough review of prior works is beyond the scope of this paper. A partial list of references relevant to the above discussion and the results of this paper is [1,7,8,9,10,6,14,18,19,20,21,23,28,26,29,30,40,43,44,46,49,50,56,57,58,60,61,62,63,64,67,76,77].…”