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+title = "Solutions to Set of all {Sets, Groups, Top. Spaces} does not exist"
+author = "Yann Herklotz"
+tags = []
+categories = []
+backlinks = ["4d"]
+forwardlinks = ["4b", "4d2"]
+zettelid = "4d1"
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+
+The problem in Set Theory ([\#4b]) and the other spaces and collections,
+is that one cannot build a collection of all collections. In Category
+Theory, one has the same problem, not being able to have a Category of
+all Categories. There are various possible solutions to this:
+
+-   Bound the size of objects by cardinal κ.
+-   Use Classes (from Set Theory: Sets that satisfy first order
+    formula).
+-   Grothendiek Universes (similar to bounding the size).
+-   Ignore the problem (possible for simple category theory).
+
+  [\#4b]: /zettel/4b