
theorem Th168:
Sum digits(15,10) = 6
proof
  thus Sum digits(15,10) = Sum <%5%>+Sum <%1%> by Th167,AFINSQ_2:55
  .= 5 + Sum <%1%> by AFINSQ_2:53
  .= 5+1 by AFINSQ_2:53
  .= 6;
end;
