
theorem Th801:
Sum digits(968,10) = 23
proof
  thus Sum digits(968,10) = Sum <%8,6%>+Sum <%9%> by Th800,AFINSQ_2:55
  .= (8 + 6) + Sum <%9%> by AFINSQ_2:54
  .= 14 + 9 by AFINSQ_2:53
  .= 23;
end;
