
theorem Th284:
Sum digits(57,10) = 12
proof
  thus Sum digits(57,10) = Sum <%7%>+Sum <%5%> by Th283,AFINSQ_2:55
  .= 7 + Sum <%5%> by AFINSQ_2:53
  .= 7+5 by AFINSQ_2:53
  .= 12;
end;
