
theorem Th511:
Sum digits(1820,10) = 11
proof
  thus Sum digits(1820,10) = Sum <%0,2,8%>+Sum <%1%> by Th510,AFINSQ_2:55
  .= Sum <%0,2%> + Sum <%8%> + Sum <%1%> by AFINSQ_2:55
  .= (0 + 2) + Sum <%8%> + Sum <%1%> by AFINSQ_2:54
  .= (0 + 2 + 8) + Sum <%1%> by AFINSQ_2:53
  .= 10 + 1 by AFINSQ_2:53
  .= 11;
end;
