
theorem Th523:
Sum digits(1940,10) = 14
proof
  thus Sum digits(1940,10) = Sum <%0,4,9%>+Sum <%1%> by Th522,AFINSQ_2:55
  .= Sum <%0,4%> + Sum <%9%> + Sum <%1%> by AFINSQ_2:55
  .= (0 + 4) + Sum <%9%> + Sum <%1%> by AFINSQ_2:54
  .= (0 + 4 + 9) + Sum <%1%> by AFINSQ_2:53
  .= 13 + 1 by AFINSQ_2:53
  .= 14;
end;
