  One of the natural ways to prove that the Hall words (Philip Hall, 1933)
consist of a basis of a free Lie algebra is a direct construction: to start
with a linear space spanned by Hall words, to define the Lie product of Hall
words, and then to check that the product yields the Lie identities (Marshall
Hall, 1950). Here we suggest another way using the Composition-Diamond lemma
for free anti-commutative (non-associative) algebras (A.I. Shirshov, 1962).
