
theorem Th553:
Sum digits(2240,10) = 8
proof
  thus Sum digits(2240,10) = Sum <%0,4,2%>+Sum <%2%> by Th552,AFINSQ_2:55
  .= Sum <%0,4%> + Sum <%2%> + Sum <%2%> by AFINSQ_2:55
  .= (0 + 4) + Sum <%2%> + Sum <%2%> by AFINSQ_2:54
  .= (0 + 4 + 2) + Sum <%2%> by AFINSQ_2:53
  .= 6 + 2 by AFINSQ_2:53
  .= 8;
end;
