
theorem Th919:
Sum digits(2398,10) = 22
proof
  thus Sum digits(2398,10) = Sum <%8,9,3%>+Sum <%2%> by Th918,AFINSQ_2:55
  .= Sum <%8,9%> + Sum <%3%> + Sum <%2%> by AFINSQ_2:55
  .= (8 + 9) + Sum <%3%> + Sum <%2%> by AFINSQ_2:54
  .= (8 + 9 + 3) + Sum <%2%> by AFINSQ_2:53
  .= 20 + 2 by AFINSQ_2:53
  .= 22;
end;
