We build a differential calculus for subalgebras of the Moyal algebra on R^4
starting from a redundant differential calculus on the Moyal algebra, which is
suitable for reduction. In some cases we find a frame of 1-forms which allows
to realize the complex of forms as a tensor product of the noncommutative
subalgebras with the external algebra Lambda^*.Comment: 13 pages, no figures. One reference added, minor correction