
theorem Th713:
Sum digits(3840,10) = 15
proof
  thus Sum digits(3840,10) = Sum <%0,4,8%>+Sum <%3%> by Th712,AFINSQ_2:55
  .= Sum <%0,4%> + Sum <%8%> + Sum <%3%> by AFINSQ_2:55
  .= (0 + 4) + Sum <%8%> + Sum <%3%> by AFINSQ_2:54
  .= (0 + 4 + 8) + Sum <%3%> by AFINSQ_2:53
  .= 12 + 3 by AFINSQ_2:53
  .= 15;
end;
