reserve i,j,k,x for object;

theorem Th18:
  for A being non empty set, o1,o2,o3 being Object of DiscrCat A
  st o1 <> o2 or o2 <> o3 holds (the Comp of DiscrCat A).(o1,o2,o3) = {}
proof
  let A be non empty set, o1,o2,o3 be Object of DiscrCat A;
  assume o1 <> o2 or o2 <> o3;
  then <^o1,o2^> = {} or <^o2,o3^> = {} by Def18;
  hence thesis;
end;
