
theorem Th687:
Sum digits(3580,10) = 16
proof
  thus Sum digits(3580,10) = Sum <%0,8,5%>+Sum <%3%> by Th686,AFINSQ_2:55
  .= Sum <%0,8%> + Sum <%5%> + Sum <%3%> by AFINSQ_2:55
  .= (0 + 8) + Sum <%5%> + Sum <%3%> by AFINSQ_2:54
  .= (0 + 8 + 5) + Sum <%3%> by AFINSQ_2:53
  .= 13 + 3 by AFINSQ_2:53
  .= 16;
end;
