In geometric topology, the de Rham invariant is a mod 2 invariant of a (4k+1)-dimensional manifold, that is, an element of
It can be thought of as the simply-connected symmetric L-group
and thus analogous to the other invariants from L-theory: the signature, a 4k-dimensional invariant (either symmetric or quadratic,
It is named for Swiss mathematician Georges de Rham, and used in surgery theory.
[1][2] The de Rham invariant of a (4k+1)-dimensional manifold can be defined in various equivalent ways:[3]