
theorem Th689:
Sum digits(3600,10) = 9
proof
  thus Sum digits(3600,10) = Sum <%0,0,6%>+Sum <%3%> by Th688,AFINSQ_2:55
  .= Sum <%0,0%> + Sum <%6%> + Sum <%3%> by AFINSQ_2:55
  .= (0 + 0) + Sum <%6%> + Sum <%3%> by AFINSQ_2:54
  .= (0 + 0 + 6) + Sum <%3%> by AFINSQ_2:53
  .= 6 + 3 by AFINSQ_2:53
  .= 9;
end;
