
theorem Th7:
  for L being non empty ZeroStr, p being AlgSequence of L, i being
  Element of NAT holds p.i <> 0.L implies len p >= i + 1
proof
  let L be non empty ZeroStr,p be AlgSequence of L, i be Element of NAT;
A1: len p is_at_least_length_of p by ALGSEQ_1:def 3;
  assume p.i <> 0.L;
  then len p > i by A1,ALGSEQ_1:def 2;
  hence thesis by NAT_1:13;
end;
