
theorem Th561:
Sum digits(2320,10) = 7
proof
  thus Sum digits(2320,10) = Sum <%0,2,3%>+Sum <%2%> by Th560,AFINSQ_2:55
  .= Sum <%0,2%> + Sum <%3%> + Sum <%2%> by AFINSQ_2:55
  .= (0 + 2) + Sum <%3%> + Sum <%2%> by AFINSQ_2:54
  .= (0 + 2 + 3) + Sum <%2%> by AFINSQ_2:53
  .= 5 + 2 by AFINSQ_2:53
  .= 7;
end;
