theorem Th26:
  for k, m be Nat st (k+m)-equivalent qa, qb holds k-equivalent qa , qb
proof
  let k, m be Nat;
  assume
A1: (k+m)-equivalent qa, qb;
  let w be FinSequence of IAlph;
A2: k <= k+m by NAT_1:11;
  assume len w <= k;
  then len w <= k+m by A2,XXREAL_0:2;
  hence thesis by A1;
end;
