
theorem Th1061:
Sum digits(672,10) = 15
proof
  thus Sum digits(672,10) = Sum <%2,7%>+Sum <%6%> by Th1060,AFINSQ_2:55
  .= (2 + 7) + Sum <%6%> by AFINSQ_2:54
  .= 9 + 6 by AFINSQ_2:53
  .= 15;
end;
