
theorem Th881:
Sum digits(1936,10) = 19
proof
  thus Sum digits(1936,10) = Sum <%6,3,9%>+Sum <%1%> by Th880,AFINSQ_2:55
  .= Sum <%6,3%> + Sum <%9%> + Sum <%1%> by AFINSQ_2:55
  .= (6 + 3) + Sum <%9%> + Sum <%1%> by AFINSQ_2:54
  .= (6 + 3 + 9) + Sum <%1%> by AFINSQ_2:53
  .= 18 + 1 by AFINSQ_2:53
  .= 19;
end;
