
theorem Th972:
Sum digits(713,10) = 11
proof
  thus Sum digits(713,10) = Sum <%3,1%>+Sum <%7%> by Th971,AFINSQ_2:55
  .= (3 + 1) + Sum <%7%> by AFINSQ_2:54
  .= 4 + 7 by AFINSQ_2:53
  .= 11;
end;
