
theorem Th1:
  for X be set for p be FinSequence of bool X for q be FinSequence
  of BOOLEAN holds dom MergeSequence(p,q) = dom p
proof
  let X be set;
  let p be FinSequence of bool X;
  let q be FinSequence of BOOLEAN;
  thus dom MergeSequence(p,q) = Seg len MergeSequence(p,q) by FINSEQ_1:def 3
    .= Seg len p by Def1
    .= dom p by FINSEQ_1:def 3;
end;
