[R] Vars package - specification of VAR

[herrdittmann at yahoo.co.uk]

Hi useRs,

Been estimating a VAR with two variables, using VAR() of the package "vars".

Perhaps I am missing something, but how can I include the present time t variables, i.e. for the set of equations to be:

x(t) = a1*y(t) + a2*y(t-1) + a3*x(t-1) + ...
Y(t) = a1*x(t) + a2*x(t-1) + a3*y(t-1) + ...

The types available in function VAR() allow for seasonal dummies, time trends and constant term.

But the terms

a1*y(t)
a1*x(t)

always seem to be excluded by default, thus only lagged variables enter the right side.

How can I specify VAR() such that a1*y(t) and a1*x(t) are included? 
Or would I have to estimate with lm() instead?

Many thanks in advance,

Bernd