In mathematics, or specifically, in differential topology, Ehresmann's lemma or Ehresmann's fibration theorem states that if a smooth mapping f : M → N {\displaystyle f\colon M\rightarrow N}, where M {\displaystyle M} and N {\displaystyle N} are smooth manifolds, is a surjective submersion, and a proper map,then it is a locally trivial fibration. Wikipedia