We consider Legendrian knots and links in the standard
3-dimensional contact space. In 1997 Chekanov [Ch] introduced
a new invariant for these knots. At the same time, a similar
construction was suggested by Eliashberg [E1] within the
framework of his joing work with Hofer and Givernthal on
Symplectic Field Theory ([E2],[EGH]). To a knot diagram,
they associated a differential algebra A. Its stable
isomorphism type is invariant under Legendrian isotopy of the
knot. ¶
In this paper, we introduce an additional structure on this
algebra in the case of a Legendrian link. For a link of N
components, we show that its algebra splits A =
⊕g ∈ G
Ag Here G is a free group on
(N - 1) variables. The splitting is determined by the
order of the knots and is preserved by the differential. It
gives a tool to show that some permutations of link components
are impossible to produce by Legendrian isotopy.