Invariants, a brief history
•Invariance has long history in perception.
•   Each movement we make by which we alter the appearance of objects should be thought of as an experiment desgned to test whether we have understood correctly the invariant relations of the phenomena before us, that is, their existence in definite spatial relations.
–Helmholtz, 1878
•   If invariants of the energy flux at the receptors of an organism exist, and if these invariants correspond to the permanent properties of the environment … then I think thee is new support for … a new theory of perception in psychology.
–Gibson, 1967
•In math, Erlanger program conceives geometry as study of invariant properties under a group of transformations.
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