
theorem Th1053:
Sum digits(504,10) = 9
proof
  thus Sum digits(504,10) = Sum <%4,0%>+Sum <%5%> by Th1052,AFINSQ_2:55
  .= (4 + 0) + Sum <%5%> by AFINSQ_2:54
  .= 4 + 5 by AFINSQ_2:53
  .= 9;
end;
