
theorem Th609:
Sum digits(2800,10) = 10
proof
  thus Sum digits(2800,10) = Sum <%0,0,8%>+Sum <%2%> by Th608,AFINSQ_2:55
  .= Sum <%0,0%> + Sum <%8%> + Sum <%2%> by AFINSQ_2:55
  .= (0 + 0) + Sum <%8%> + Sum <%2%> by AFINSQ_2:54
  .= (0 + 0 + 8) + Sum <%2%> by AFINSQ_2:53
  .= 8 + 2 by AFINSQ_2:53
  .= 10;
end;
