
theorem Th1376:
Sum digits(4975,10) = 25
proof
  thus Sum digits(4975,10) = Sum <%5,7,9%>+Sum <%4%> by Th1375,AFINSQ_2:55
  .= Sum <%5,7%> + Sum <%9%> + Sum <%4%> by AFINSQ_2:55
  .= (5 + 7) + Sum <%9%> + Sum <%4%> by AFINSQ_2:54
  .= (5 + 7 + 9) + Sum <%4%> by AFINSQ_2:53
  .= 21 + 4 by AFINSQ_2:53
  .= 25;
end;
