Fisher's Instrumental Approach to Index Numbers

* Marcel Boumans 'If contradictory attributes be assigned to a concept, I say, that mathematically the concept does not exist.' (Hilbert 1902, 448) 'Sometimes control with a single lens is impossible since some incompatible features are required and a compromise becomes necessary calling for further judgement on the part of the designer as to which error should be reduced and to what degree.' (Bracey 1960, 18)