reserve x,A,B,X,X9,Y,Y9,Z,V for set;

theorem
  for A,B,C,D being set st A misses D & B misses D & C misses D holds A
  \/ B \/ C misses D
proof
  let A,B,C,D be set;
  assume A misses D & B misses D;
  then
A1: A \/ B misses D by Th70;
  assume C misses D;
  hence thesis by A1,Th70;
