
theorem Th968:
Sum digits(667,10) = 19
proof
  thus Sum digits(667,10) = Sum <%7,6%>+Sum <%6%> by Th967,AFINSQ_2:55
  .= (7 + 6) + Sum <%6%> by AFINSQ_2:54
  .= 13 + 6 by AFINSQ_2:53
  .= 19;
end;
