
theorem Th719:
Sum digits(3900,10) = 12
proof
  thus Sum digits(3900,10) = Sum <%0,0,9%>+Sum <%3%> by Th718,AFINSQ_2:55
  .= Sum <%0,0%> + Sum <%9%> + Sum <%3%> by AFINSQ_2:55
  .= (0 + 0) + Sum <%9%> + Sum <%3%> by AFINSQ_2:54
  .= (0 + 0 + 9) + Sum <%3%> by AFINSQ_2:53
  .= 9 + 3 by AFINSQ_2:53
  .= 12;
end;
