Let M be a manifold with the differential d acting on exterior forms. A differential operator δ is defined by:
δ(α)=dα∧β
with β∧dβ=0, then we have δ∘δ=0. The cohomology is defined:
H∗β(M,R)=Ker(δ)/Im(δ)
Can we find new topological invariants of manifolds?