
theorem Th922:
Sum digits(23,10) = 5
proof
  thus Sum digits(23,10) = Sum <%3%>+Sum <%2%> by Th921,AFINSQ_2:55
  .= 3 + Sum <%2%> by AFINSQ_2:53
  .= 3+2 by AFINSQ_2:53
  .= 5;
end;
