
theorem Th677:
Sum digits(3480,10) = 15
proof
  thus Sum digits(3480,10) = Sum <%0,8,4%>+Sum <%3%> by Th676,AFINSQ_2:55
  .= Sum <%0,8%> + Sum <%4%> + Sum <%3%> by AFINSQ_2:55
  .= (0 + 8) + Sum <%4%> + Sum <%3%> by AFINSQ_2:54
  .= (0 + 8 + 4) + Sum <%3%> by AFINSQ_2:53
  .= 12 + 3 by AFINSQ_2:53
  .= 15;
end;
