  Following a seminar the present author gave to an Automata Theory course to
computer science students, it will be presented, in a very synthetic and mostly
selfcontained way, the principal properties of context free languages (CFL),
with particular attention given to the Pumping Lemma (PL), and of grammars
which generate them(CFG). We refer to Chomsky and Schutzenberger for the first
works about it. What is known in literature as the Iteration Theorem here will
be referred to as the Ogden's Lemma in a fully justified way. All definitions
not strictly connected with the notion of context freeness will be omitted (we
will give precise references for all of them). The symbology used is
substantially the classical one, but we will replace some symbols to avoid
confusion with those used in logic
