
theorem Th681:
Sum digits(3520,10) = 10
proof
  thus Sum digits(3520,10) = Sum <%0,2,5%>+Sum <%3%> by Th680,AFINSQ_2:55
  .= Sum <%0,2%> + Sum <%5%> + Sum <%3%> by AFINSQ_2:55
  .= (0 + 2) + Sum <%5%> + Sum <%3%> by AFINSQ_2:54
  .= (0 + 2 + 5) + Sum <%3%> by AFINSQ_2:53
  .= 7 + 3 by AFINSQ_2:53
  .= 10;
end;
