
theorem Th803:
Sum digits(990,10) = 18
proof
  thus Sum digits(990,10) = Sum <%0,9%>+Sum <%9%> by Th802,AFINSQ_2:55
  .= (0 + 9) + Sum <%9%> by AFINSQ_2:54
  .= 9 + 9 by AFINSQ_2:53
  .= 18;
end;
