
theorem Th1338:
Sum digits(4500,10) = 9
proof
  thus Sum digits(4500,10) = Sum <%0,0,5%>+Sum <%4%> by Th1337,AFINSQ_2:55
  .= Sum <%0,0%> + Sum <%5%> + Sum <%4%> by AFINSQ_2:55
  .= (0 + 0) + Sum <%5%> + Sum <%4%> by AFINSQ_2:54
  .= (0 + 0 + 5) + Sum <%4%> by AFINSQ_2:53
  .= 5 + 4 by AFINSQ_2:53
  .= 9;
end;
