Floer's paper, An InstantonInvariant for 3Manifolds, makes reference to Casson's construction of a topological invariant for homology 3spheres. He literally references it by placing the bibliographictag [C] in one of his sentences... but he doesn't actually list it in the bibliography!
I subsequently search around, and cannot find where Casson originally defines his invariant; only locate papers that talk about his invariant. Does this "paper" not exist? I would think that such an important construction has a foundational paper in existence.



According to the following paper, this invariant's introduction is sourced as: A. Casson, Lecture notes, MSRI Lectures, Berkeley, 1985. The first published discussion appears to be found in: S. Akbulut & J. McCarthy, Casson's invariant for oriented homology 3spheres, an exposition, Math. Notes, No. 36, Princeton Univ. Press, Princeton, 1990. "I don't know if he [Casson] has ever written his notes. I attended his lectures at MSRI then I went back to MSU and tried to fill in the details together with McCarthy, those notes are the result." S. Akbulut "Here is a pdf of handwritten notes of T. Cochran's. Page two includes annotated notes by Boyer, and I got the notes from my friend and colleague, A. Nicas." H. Boden 

