Building on work of Huntington (1933), Robbins conjectured that the equations for a Robbins algebra, commutativity,
associativity, and the Robbins Equation
References
Huntington, E. V. ``New Sets of Independent Postulates for the Algebra of Logic, with Special Reference
to Whitehead and Russell's Principia Mathematica.'' Trans. Amer. Math. Soc. 35, 274-304, 1933.
Huntington, E. V. ``Boolean Algebra. A Correction.'' Trans. Amer. Math. Soc. 35, 557-558, 1933.
McCune, W. ``Solution of the Robbins Problem.'' J. Automat. Reason. 19, 263-276, 1997.
McCune, W. ``Robbins Algebras are Boolean.''
http://www-unix.mcs.anl.gov/~mccune/papers/robbins/.
Nelson, E. ``Automated Reasoning.'' http://www.math.princeton.edu/~nelson/ar.html.