
theorem Th324:
Sum digits(551,10) = 11
proof
  thus Sum digits(551,10) = Sum <%1,5%>+Sum <%5%> by Th323,AFINSQ_2:55
  .= (1 + 5) + Sum <%5%> by AFINSQ_2:54
  .= 6 + 5 by AFINSQ_2:53
  .= 11;
end;
