
theorem Th1065:
Sum digits(744,10) = 15
proof
  thus Sum digits(744,10) = Sum <%4,4%>+Sum <%7%> by Th1064,AFINSQ_2:55
  .= (4 + 4) + Sum <%7%> by AFINSQ_2:54
  .= 8 + 7 by AFINSQ_2:53
  .= 15;
end;
