theorem Th68:
  len f <= n implies Ins(f,n,p) = f^<*p*>
proof
  assume
A1: len f <= n;
  then f/^n is empty by Th32;
  hence Ins(f,n,p) = (f|n)^<*p*> by FINSEQ_1:34
    .= f^<*p*> by A1,FINSEQ_1:58;
end;
