
theorem Th980:
Sum digits(805,10) = 13
proof
  thus Sum digits(805,10) = Sum <%5,0%>+Sum <%8%> by Th979,AFINSQ_2:55
  .= (5 + 0) + Sum <%8%> by AFINSQ_2:54
  .= 5 + 8 by AFINSQ_2:53
  .= 13;
end;
