
theorem Th813:
Sum digits(1122,10) = 6
proof
  thus Sum digits(1122,10) = Sum <%2,2,1%>+Sum <%1%> by Th812,AFINSQ_2:55
  .= Sum <%2,2%> + Sum <%1%> + Sum <%1%> by AFINSQ_2:55
  .= (2 + 2) + Sum <%1%> + Sum <%1%> by AFINSQ_2:54
  .= (2 + 2 + 1) + Sum <%1%> by AFINSQ_2:53
  .= 5 + 1 by AFINSQ_2:53
  .= 6;
end;
