
theorem Th280:
Sum digits(19,10) = 10
proof
  thus Sum digits(19,10) = Sum <%9%>+Sum <%1%> by Th279,AFINSQ_2:55
  .= 9 + Sum <%1%> by AFINSQ_2:53
  .= 9+1 by AFINSQ_2:53
  .= 10;
end;
