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Published online by Cambridge University Press: 20 November 2018
The simplest examples of figures which possess inner orientation are a sensed line, and a plane in which a sense of rotation is specified. Suppose two sensed lines, which intersect in a finite point, are given in a definite order. Then there is only one way in which the first can be rotated to coincide with the second without passing through the second. In this way, two ordered, sensed lines determine a sense of rotation in the plane which contains them.