thus Sum (digits (2222,10)) = (Sum <%2,2,2%>) + (Sum <%2%>) by Th902, AFINSQ_2:55
.= ((Sum <%2,2%>) + (Sum <%2%>)) + (Sum <%2%>) by AFINSQ_2:55
.= ((2 + 2) + (Sum <%2%>)) + (Sum <%2%>) by AFINSQ_2:54
.= ((2 + 2) + 2) + (Sum <%2%>) by AFINSQ_2:53
.= 6 + 2 by AFINSQ_2:53
.= 8 ; :: thesis: verum