reserve x,y,z for object,
  i,j,n,m for Nat,
  D for non empty set,
  s,t for FinSequence,
  a,a1,a2,b1,b2,d for Element of D,
  p, p1,p2,q,r for FinSequence of D;

theorem Th4:
  for s1,s2 be FinSequence st len s1 =n & len s2 = n holds <*s1,s2
  *> is tabular
proof
  let s1,s2 be FinSequence;
  assume
A1: len s1 =n & len s2 =n;
    take n;
    let x;
    assume x in rng (<*s1,s2*>);
    then
A2: x in { s1,s2} by FINSEQ_2:127;
    then reconsider r=x as FinSequence by TARSKI:def 2;
    take r;
    thus x= r & len r=n by A1,A2,TARSKI:def 2;
end;
