I suppose this is not hard, but I thought quite a time about it and don't get what the point is.
I'm reading Deligne's "Equations differentielles...", where he defines what a Grothendieck Connection is:
you consider a smooth projective variety $X$ over the complex numbers and a coherent sheaf $F$ on it. Let $X_1$ be the first infinitesimal neighborhood of the diagonal of $X$ and $p_1,p_2$ the two projections of $X_1$ to $X$.
Then one defines a connection as a homomorphism $p_1^*F \rightarrow p_2^*F$, which restricts to the identiy on $X$.
Deligne says in a bracket that such a homomorphism is always an isomorphism. What's the reason for this?
Addition: can one formulate a general principle, which roughly says that if I have a homomorphism on the first oder neighborhood of the diagonal, which is an iso on $X$, then it is already an iso? How general does something like this hold?