
theorem Th413:
Sum digits(840,10) = 12
proof
  thus Sum digits(840,10) = Sum <%0,4%>+Sum <%8%> by Th412,AFINSQ_2:55
  .= (0 + 4) + Sum <%8%> by AFINSQ_2:54
  .= 4 + 8 by AFINSQ_2:53
  .= 12;
end;
