
theorem Th40:
  for L be non empty ZeroStr for z0,z1 be Element of L st z1 <> 0.
  L holds len <%z0,z1%> = 2
proof
  let L be non empty ZeroStr;
  let z0,z1 be Element of L;
  assume z1 <> 0.L;
  then <%z0,z1%>.1 <> 0.L by Th38;
  then
A1: for n be Nat st n is_at_least_length_of <%z0,z1%> holds 1+1 <= n
    by NAT_1:13;
  2 is_at_least_length_of <%z0,z1%> by Th38;
  hence thesis by A1,ALGSEQ_1:def 3;
end;
