
theorem Th238:
Sum digits(153,10) = 9
proof
  thus Sum digits(153,10) = Sum <%3,5%>+Sum <%1%> by Th237,AFINSQ_2:55
  .= (3 + 5) + Sum <%1%> by AFINSQ_2:54
  .= 8 + 1 by AFINSQ_2:53
  .= 9;
end;
