
theorem Th423:
Sum digits(940,10) = 13
proof
  thus Sum digits(940,10) = Sum <%0,4%>+Sum <%9%> by Th422,AFINSQ_2:55
  .= (0 + 4) + Sum <%9%> by AFINSQ_2:54
  .= 4 + 9 by AFINSQ_2:53
  .= 13;
end;
