
theorem Th789:
Sum digits(792,10) = 18
proof
  thus Sum digits(792,10) = Sum <%2,9%>+Sum <%7%> by Th788,AFINSQ_2:55
  .= (2 + 9) + Sum <%7%> by AFINSQ_2:54
  .= 11 + 7 by AFINSQ_2:53
  .= 18;
end;
