  This paper contains an elementary proof of the existence of the classical
model structure on the category of unbounded DG-Lie algebras over a field of
characteristic zero, with an emphasis on the properties of free and semifree
extensions, which are particularly nice cofibrations. The cobar construction of
a locally conilpotent cocommutative coalgebra is shown to be an example of
semifree DG-Lie algebra. We also give an example of a non-cofibrant DG-Lie
algebra whose underlying graded Lie algebra is free; this cannot occur in the
bounded above case, where DG-Lie algebras of this form are always cofibrant.
