
theorem Th153:
Sum digits(168,10) = 15
proof
  thus Sum digits(168,10) = Sum <%8,6%>+Sum <%1%> by Th152,AFINSQ_2:55
  .= (8 + 6) + Sum <%1%> by AFINSQ_2:54
  .= 14 + 1 by AFINSQ_2:53
  .= 15;
end;
