
theorem Th545:
Sum digits(2160,10) = 9
proof
  thus Sum digits(2160,10) = Sum <%0,6,1%>+Sum <%2%> by Th544,AFINSQ_2:55
  .= Sum <%0,6%> + Sum <%1%> + Sum <%2%> by AFINSQ_2:55
  .= (0 + 6) + Sum <%1%> + Sum <%2%> by AFINSQ_2:54
  .= (0 + 6 + 1) + Sum <%2%> by AFINSQ_2:53
  .= 7 + 2 by AFINSQ_2:53
  .= 9;
end;
