
theorem Th547:
Sum digits(2180,10) = 11
proof
  thus Sum digits(2180,10) = Sum <%0,8,1%>+Sum <%2%> by Th546,AFINSQ_2:55
  .= Sum <%0,8%> + Sum <%1%> + Sum <%2%> by AFINSQ_2:55
  .= (0 + 8) + Sum <%1%> + Sum <%2%> by AFINSQ_2:54
  .= (0 + 8 + 1) + Sum <%2%> by AFINSQ_2:53
  .= 9 + 2 by AFINSQ_2:53
  .= 11;
end;
