
theorem Th130:
Sum digits(221,10) = 5
proof
  thus Sum digits(221,10) = Sum <%1,2%>+Sum <%2%> by Th129,AFINSQ_2:55
  .= (1 + 2) + Sum <%2%> by AFINSQ_2:54
  .= 3 + 2 by AFINSQ_2:53
  .= 5;
end;
