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has recently studied the following mapping . In projective 4 -space P^ two planes t^ and r^ are given, intersecting at the point T. A projecting plane 9 is defined as a plane through T intersecting both r^ and z^ in a straight line. It is shown that through a point A of P^ passes, in general, one projecting plane 9(A). A projection plane ir is introduced, not passing through T, and intersecting r1 at T^' (i=1,2). The projection A' of A onto ir is defined as the intersection of 9(A) and jr.doi:10.1515/dema-1979-0414 fatcat:64xoliuyuzb4reyvvta6m7hbbe