Many thanks @Indian for your back links. The crucial element retains in site 181 of the first one particular, when describing the generative grammar of webpage a hundred and eighty: "If a is specified and also a will not be specified, then Internal is implicit." يَتْبَعُيَتْبَعُ، يَسيرُ وراءيَتَّبِعُ، يُطيعيَسْلُك طريقا، https://daveyg541dgg2.blogunteer.com/profile