theorem
  w1 in Z_Lin{w1,w2,w3} & w2 in Z_Lin{w1,w2,w3} & w3 in Z_Lin{w1,w2,w3}
proof
A1: w3 in {w1,w2,w3} by ENUMSET1:def 1;
  w1 in {w1,w2,w3} & w2 in {w1,w2,w3} by ENUMSET1:def 1;
  hence thesis by A1,Th12;
end;
