reserve k,n for Nat,
  x,y,z,y1,y2 for object,X,Y for set,
  f,g for Function;
reserve p,q,r,s,t for XFinSequence;
reserve D for set;

theorem :: FINSEQ_2:7
   n <len p implies (p^q).n=p.n
proof
  assume n <len p;
  then n in dom p by Lm1;
  hence thesis by Def3;
end;
