Transformations Which are Products of Two Involutions Maria Wonenburger Indiana University Mathematics Journal 1967 text pdf 10.1512/iumj.1967.16.16023 10.1512/iumj.1967.16.16023 en Indiana Univ. Math. J. 16 (1967) 327 - 338 state-of-the-art mathematics http://iumj.org/access/