
theorem Th411:
Sum digits(820,10) = 10
proof
  thus Sum digits(820,10) = Sum <%0,2%>+Sum <%8%> by Th410,AFINSQ_2:55
  .= (0 + 2) + Sum <%8%> by AFINSQ_2:54
  .= 2 + 8 by AFINSQ_2:53
  .= 10;
end;
