
theorem Th271:
Sum digits(54,10) = 9
proof
  thus Sum digits(54,10) = Sum <%4%>+Sum <%5%> by Th270,AFINSQ_2:55
  .= 4 + Sum <%5%> by AFINSQ_2:53
  .= 4+5 by AFINSQ_2:53
  .= 9;
end;
