t of X.
| We say that Y is &quot;locally closed&quot; in X if every point
| y in Y has an open neighborhood U in X such that Y |^| U
| is closed in U.  One verifies easily that a locally closed
| subset is the intersection of an open set and a closed set.
| For instance, any open subset of X is locally closed, and
| any open interval is locally closed in the plane.
|
| Let X be a manifold (of class C^p with p &gt;= 0).  Let Y be a subset of X
| and assume that for each point y in Y there exists a chart (V, 