reserve X,Y,Z,Z1,Z2,D for set,x,y for object;
reserve SFX,SFY,SFZ for set;
reserve F,G for Subset-Family of D;
reserve P for Subset of D;
reserve E for set;

theorem Th46:
  {{}} is Subset-Family of X
proof
  {} c= X;
  hence thesis by ZFMISC_1:31;
end;
