Proper Class
See also
Ordinal Number, Set, Set ClassExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Proper Class." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/ProperClass.html
Weisstein, Eric W. "Proper Class." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/ProperClass.html