redefine attr T is T_0 means :: T_0TOPSP:def 7 ( T : ( ( ) ( ) set ) is empty or for x, y being ( ( ) ( ) Point of ( ( ) ( ) set ) ) st x : ( ( ) ( ) Point of ( ( ) ( ) set ) ) <> y : ( ( ) ( ) Point of ( ( ) ( ) set ) ) holds ex V being ( ( ) ( ) Subset of ) st ( V : ( ( ) ( ) Subset of ) is open & ( ( x : ( ( ) ( ) Point of ( ( ) ( ) set ) ) in V : ( ( ) ( ) Subset of ) & not y : ( ( ) ( ) Point of ( ( ) ( ) set ) ) in V : ( ( ) ( ) Subset of ) ) or ( y : ( ( ) ( ) Point of ( ( ) ( ) set ) ) in V : ( ( ) ( ) Subset of ) & not x : ( ( ) ( ) Point of ( ( ) ( ) set ) ) in V : ( ( ) ( ) Subset of ) ) ) ) );