
theorem Th497:
Sum digits(1680,10) = 15
proof
  thus Sum digits(1680,10) = Sum <%0,8,6%>+Sum <%1%> by Th496,AFINSQ_2:55
  .= Sum <%0,8%> + Sum <%6%> + Sum <%1%> by AFINSQ_2:55
  .= (0 + 8) + Sum <%6%> + Sum <%1%> by AFINSQ_2:54
  .= (0 + 8 + 6) + Sum <%1%> by AFINSQ_2:53
  .= 14 + 1 by AFINSQ_2:53
  .= 15;
end;
