
theorem Th723:
Sum digits(3940,10) = 16
proof
  thus Sum digits(3940,10) = Sum <%0,4,9%>+Sum <%3%> by Th722,AFINSQ_2:55
  .= Sum <%0,4%> + Sum <%9%> + Sum <%3%> by AFINSQ_2:55
  .= (0 + 4) + Sum <%9%> + Sum <%3%> by AFINSQ_2:54
  .= (0 + 4 + 9) + Sum <%3%> by AFINSQ_2:53
  .= 13 + 3 by AFINSQ_2:53
  .= 16;
end;
