Let $M$ be an $n$-dimensional manifold. A distribution $D$ on $M$ is an assignment of a subspace $D_m \subset T_mM$ for each $m\in M$. A vector field $X$ on M belongs to $D$ if $X_m \in D_m$, for all $m\in M$. A distribution $D$ is said to be involutive if $[X,Y]\in D$ for all $X,Y\in D$. A distribution $D$ is called non-singular if for all $m\in M$, there exist an open neighborhood $U$ of $m$ such that the dimension of $D$ is constant on $U$.
Under which conditions is a non-singular distribution involutive?