
theorem Th777:
Sum digits(638,10) = 17
proof
  thus Sum digits(638,10) = Sum <%8,3%>+Sum <%6%> by Th776,AFINSQ_2:55
  .= (8 + 3) + Sum <%6%> by AFINSQ_2:54
  .= 11 + 6 by AFINSQ_2:53
  .= 17;
end;
