What literary features are involved in Jean-Paul Sartre's No Exit?

Jean-Paul Sartre's No Exit follows
the classical rules of unity, action, and place.  As a one-act play, there is, of
course, unity. And, with a singleness of setting, everything works towards one end, one
purpose. Its existential theme is the single focus of this philosophical play as the
psychological states of the characters and the objects in the room point to the symbolic
significance of Sartre's work.

The inability to blink, to
close one's eyes in sleep, and escape from reality, leads Garcin to utter the
metaphorical remark, "So one has to live with one's eyes open all the time?"  Faced with
an existence stripped of all delusion, the three characters must, at last, sort out
their being from the visions they have had and try to find their own existential
uniqueness and define it as it will be for eternity.  They cannot escape from this
existential task because there is "no exit." But, since they must see themselves only in
the eyes of the other without glass or mirror,

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And deep down in my eyes you'll see yourself just
as you want to be. 

there is
no way to exist as an individual. The bell, which does not always ring, represents their
only connection with the outside world.  The open door has been an opportunity for them
to escape, but are too weak to face the consequences of freedom.  Now, they are
confronted for eternity with each other. The symbolic paper knife is used by Estelle in
a futile attempt to escape her fate with Inez; however, she, like Garcin concludes,
"Hell--is other people."  They sit and ponder the consequences of their inauthentic
existences in life, and their eternal inability to forge any individual
essence.