
theorem Th657:
Sum digits(3280,10) = 13
proof
  thus Sum digits(3280,10) = Sum <%0,8,2%>+Sum <%3%> by Th656,AFINSQ_2:55
  .= Sum <%0,8%> + Sum <%2%> + Sum <%3%> by AFINSQ_2:55
  .= (0 + 8) + Sum <%2%> + Sum <%3%> by AFINSQ_2:54
  .= (0 + 8 + 2) + Sum <%3%> by AFINSQ_2:53
  .= 10 + 3 by AFINSQ_2:53
  .= 13;
end;
