removed empty chapter (#3602)

Author: GinoGiotto

set.mm

@@ -24638,13 +24638,6 @@ number of additional axioms (mainly to replace definitions like ~ df-or and
 $)
 
 
-$(
-#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#
-  Zermelo-Fraenkel Set Theory
-#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#
-$)
-
-
 $(
 #*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#
   ZF Set Theory - start with the Axiom of Extensionality