Abstract. We describe an algorithm which allows one to compute the local formulas for first and second operators in the nonlinear first Spencer sequence up to any order. We then indicate how to construct the dual sequence which is related to the original sequence by a commutative diagram where the vertical arrows are induced by the inversion in the jet group. We hope that our approach will uncover the elementary nature of this sequence which has recently shown to be relevant in physics and also has some remarkable relations to connections and make it accessible to a larger audience.
Keywords. Jets, Spencer Sequence