It is only a slight extension of the idea of "obviousness" and one supported by precedent to reach the fourth concept: "merger." If a particular expression is one of a quite limited number of the possible ways of expressing an idea, then, under this fourth concept, the expression is not copyrightable: .

             When the uncopyrightable subject matter is very narrow, so that "the topic necessarily requires," if not only one form of expression, at best only a limited number, to permit copyrighting would mean that a party or parties, by copyrighting a mere handful of forms, could exhaust all possibility of future use of the substance. In such circumstances it does not seem accurate to say .

             that any particular form of expression comes from the subject matter. However, it is necessary to say that the subject matter would be appropriated by permitting the copyrighting of its expression. We cannot recognize copyright as a game of chess in which the public can be checkmated. .

             When there is essentially only one way to express an idea, the idea and its expression are inseparable and copyright is no bar to copying that expression. If, however, the expression of an idea has elements that go beyond all functional elements of the idea itself, and beyond the obvious, and if there are numerous other ways of expressing the noncopyrightable idea, then those elements of expression, if original and substantial, are copyrightable. .

             f) The Legal Test for Copyrightability .

             Keeton J then proceeded to lay down the legal test for copyrightability. His main concern here was not with originality or fixation in a tangible form but with the idea-expression distinction. He explained that "one among the principal elements to be weighed in determining copyrightability when the ideaexpression distinction applies is to conceive and define the idea in a way that places it somewhere along the scale of abstraction (somewhere between the most abstract and the most specific of all possible conceptions).