I was learning Sheaf theory over past few weeks. Recently, I was told that the Mayer-Vietoris sequences in homology theory is actually a sheaf theoretic result. I was surprised by this information and, would like to know more about this connection. Can any of you explain me how we obtain Mayer-Vietoris using the sheaf condition?
I was thinking about Mayer–Vietoris sequence as the analogue of Seifert–van Kampen theorem for homology. This make me wonder whether the Seifert–van Kampen is also a sheaf theoretic result?