
theorem Th783:
Sum digits(726,10) = 15
proof
  thus Sum digits(726,10) = Sum <%6,2%>+Sum <%7%> by Th782,AFINSQ_2:55
  .= (6 + 2) + Sum <%7%> by AFINSQ_2:54
  .= 8 + 7 by AFINSQ_2:53
  .= 15;
end;
