I have heard this many times that "FD is a special case of FE" and separately, that "FV is a special case of FE".
However I have never come across a brief document that substantiates that claim, through derivation, examples, proofs, whatever.
I understand the basics of FE and the 3 manifestations: Collocation, Least-squares, Galerkin.
I also understand that these three can be considered as various kinds of "weighted residual" schemes, and the unifying principle is MWR (method of weighted residuals) which is a variational method.
Are there two easy-to-read resources, one for FD and one for FV, that can make the connection to either FE or MWR or something like that?