
theorem Th617:
Sum digits(2880,10) = 18
proof
  thus Sum digits(2880,10) = Sum <%0,8,8%>+Sum <%2%> by Th616,AFINSQ_2:55
  .= Sum <%0,8%> + Sum <%8%> + Sum <%2%> by AFINSQ_2:55
  .= (0 + 8) + Sum <%8%> + Sum <%2%> by AFINSQ_2:54
  .= (0 + 8 + 8) + Sum <%2%> by AFINSQ_2:53
  .= 16 + 2 by AFINSQ_2:53
  .= 18;
end;
