Carl Theodore Heisel

Carl Theodore Heisel (1852–1937)^[1] was a mathematical crank who wrote several books in the 1930s challenging accepted mathematical truths. Among his claims is that he found a way to square the circle. He is credited with 24 works in 62 publications.^[2] Heisel did not charge money for his books; he gave thousands of them away for free. Because of this, they are available at many libraries and universities. Heisel's books have historic and monetary value.^[3] Paul Halmos referred to one of Heisel's works as a "classic crank book."^[4]

Selected works

• Heisel, Carl Theodore (1934). Mathematical and geometrical demonstrations, disproving numerous theorems, problems, postulates, corolleries, axioms naturally growing out of the extraordinary discoveries of a lacking link (2d. ed.). Cleveland.