 Thus, structured representations have a concatenative structure: each token of a structured representation involves a concatenation of tokens of the constituent representations. Connectionists who deny (vi) espouse a non-concatenative conception of constituency structure, according to which structure is encoded by a suitable distributed representation. Developments of the non-concatenative conception are usually quite technical (Elman 1989; Hinton 1990; Pollack 1990; Smolensky 1990, 1991, 1995; Touretzky 1990). Most models use vector or tensor algebra to define operations over connectionist representations, which are codified by activity vectors across nodes in a neural network. The representations are said to have implicit constituency structure: the constituents are not literal parts of the complex representation, but they can be extracted from the complex representation through suitable computational operations over it.