
theorem Th273:
Sum digits(72,10) = 9
proof
  thus Sum digits(72,10) = Sum <%2%>+Sum <%7%> by Th272,AFINSQ_2:55
  .= 2 + Sum <%7%> by AFINSQ_2:53
  .= 2+7 by AFINSQ_2:53
  .= 9;
end;
