I am looking for a bibliographic source for a course on external differential calculus that is accessible at a very "low level" in university; first or second year of university in physics and chemistry; no more. Is there a course that very simply introduces the notions of external differential calculus, in the least formal way possible mathematically and in the most quickly exploitable and understandable almost intuitively. Included in this course are the Frobenius theorem and the non-integrable differentiable systems according to this theorem .
Thank you in advance