
theorem Th1374:
Sum digits(4950,10) = 18
proof
  thus Sum digits(4950,10) = Sum <%0,5,9%>+Sum <%4%> by Th1373,AFINSQ_2:55
  .= Sum <%0,5%> + Sum <%9%> + Sum <%4%> by AFINSQ_2:55
  .= (0 + 5) + Sum <%9%> + Sum <%4%> by AFINSQ_2:54
  .= (0 + 5 + 9) + Sum <%4%> by AFINSQ_2:53
  .= 14 + 4 by AFINSQ_2:53
  .= 18;
end;
