
theorem Th557:
Sum digits(2280,10) = 12
proof
  thus Sum digits(2280,10) = Sum <%0,8,2%>+Sum <%2%> by Th556,AFINSQ_2:55
  .= Sum <%0,8%> + Sum <%2%> + Sum <%2%> by AFINSQ_2:55
  .= (0 + 8) + Sum <%2%> + Sum <%2%> by AFINSQ_2:54
  .= (0 + 8 + 2) + Sum <%2%> by AFINSQ_2:53
  .= 10 + 2 by AFINSQ_2:53
  .= 12;
end;
