Research on comparable devices was also being done in other places such as SRI, and many researchers had big expectations on what they could do. The initial excitement became somewhat reduced, though, when in 1969 Marvin Minsky and Seymour Papert published the book “Perceptrons” with a mathematical proof about the limitations of two-layer feed-forward perceptrons as well as unproven claims about the difficulty of training multi-layer perceptrons. The book's only proven result—that linear functions cannot model non-linear ones—was trivial but the book had nevertheless a pronounced effect on research funding and, consequently, the community.