
theorem Th717:
Sum digits(3880,10) = 19
proof
  thus Sum digits(3880,10) = Sum <%0,8,8%>+Sum <%3%> by Th716,AFINSQ_2:55
  .= Sum <%0,8%> + Sum <%8%> + Sum <%3%> by AFINSQ_2:55
  .= (0 + 8) + Sum <%8%> + Sum <%3%> by AFINSQ_2:54
  .= (0 + 8 + 8) + Sum <%3%> by AFINSQ_2:53
  .= 16 + 3 by AFINSQ_2:53
  .= 19;
end;
