"Marks of Existence" and "Gates To Enlightenment", are they Same? Three gates and Four marks  are shown using these tearms -Impermanence,  Suffering, Non-self, Voidness, Nirvana,Shunyata (Emptiness). 

Some questions discuss them separatly. But some conflicts can see.

Quote from FullPeaceOrg


  The Three marks of existence (Pali: tilakkhaṇa; Sanskrit: trilakṣaṇa),
  are these three characteristics (Theravada)

Impermanence (Anicca)
Suffering or unsatisfactoriness (Dukkha)
Non-self or not-self (Anatta)

  
  This is a central teaching in Buddhism - completely understanding
  these three leads to the liberation of Nirvana/Nibbana. All sentient
  beings experience these marks of existence


Quote from Andrei


  In an interesting twist, my present teacher, who comes from a
  Taoism-influenced non-sectarian tradition, speaks of Three Gates To
  Enlightenment, the experiential realizations one must go through on
  one's way to Completion:
  
  
  Pain or Suffering. One must realize that life is painful and accept pain as necessary condition for one's growth. This involves
  dropping resistance that comes from seeing pain as important factor of
  one's decisions.
  Impermanence or Transience. One must fully accept that nothing is permanent in one's life, and admit the inevitability of death. This
  involves dropping attachments to what one holds as dear.
  Nothingness or Voidness. One must go through the realization that life is pointless and has no meaning in the absolute sense. This
  involves dropping fundamental preconceptions or imperatives about the
  purpose of one's life.
  


Quote from Three Marks of Mahayana


  Most of the time in Mahayana (both Vajrayana and Zen) I hear of  Four Marks of Existence: Transience, Unsatisfactoriness, Corelessness, and
  Nirvana. All four are subsumed under Shunyata (Emptiness) which is
  equated with Pratitya-Samutpada (Dependent Co-Arising).


Is something missing there?
Is there any common agreement?
Pretty generally speaking, realising the truth is enlightenment. So if the three(or four) marks of existence are true then realising them would be the gates to enlightenment.
The different sects of buddhism are forming distinct views and belief systems, which is not wise, this is what results in very confusing and difficult reading.