func (l *List) PushBackElement(e *Element) *Element {
	e.Next = nil
	if l.N == 0 {
		l.head = e
	} else {
		l.tail.Next = e
	}
	l.tail = e
	l.N++
	return e
}
//PushBackElement inserts an existing element at the back of list l and returns e.

PushBackElement inserts an existing element at the back of list l and returns e.
// PushBackElement inserts an existing element at the back of list l and returns e .
func (l *List) PushBackElement(e *Element) *Element {
	e.Next = nil
	if l.N == 0 {
		l.head = e
	} else {
		l.tail.Next = e
	}
	l.tail = e
	l.N++
	return e
}
func ( l * List ) PushBackElement ( e * Element ) * Element { e . Next = nil if l . N == 0 { l . head = e } else { l . tail . Next = e } l . tail = e l . N ++ return e }
PushBackElement inserts an existing element at the back of list l and returns e.
PushBackElement inserts an existing element at the back of list l and returns e .