Apparently, this user prefers to keep an air of mystery about them.
19 Are Conway's omnific integers the Grothendieck group of the ordinals under commutative addition? jul 25 '12
13 What's the difference between ZFC+Grothendieck, ZFC+inaccessible cardinals and Tarski-Grothendieck set theory? jul 22 '12
7 Surreal numbers, ultrapowers of $\Bbb R$, ordinal-valued functions and the slow-growing hierarchy feb 8 '14