
theorem Th403:
Sum digits(720,10) = 9
proof
  thus Sum digits(720,10) = Sum <%0,2%>+Sum <%7%> by Th402,AFINSQ_2:55
  .= (0 + 2) + Sum <%7%> by AFINSQ_2:54
  .= 2 + 7 by AFINSQ_2:53
  .= 9;
end;
