
theorem Th1294:
Sum digits(3950,10) = 17
proof
  thus Sum digits(3950,10) = Sum <%0,5,9%>+Sum <%3%> by Th1293,AFINSQ_2:55
  .= Sum <%0,5%> + Sum <%9%> + Sum <%3%> by AFINSQ_2:55
  .= (0 + 5) + Sum <%9%> + Sum <%3%> by AFINSQ_2:54
  .= (0 + 5 + 9) + Sum <%3%> by AFINSQ_2:53
  .= 14 + 3 by AFINSQ_2:53
  .= 17;
end;
