1. We remind the reader of Wemark's terminological distinction between the money-metric or the minimum income function, as it is being termed here, and the expenditure function. Weymark also notes that that the transformation function is also known as the distance or gauge function. Also, see Deaton;References Primary Sources: 1961 and Before 93,1986
2. The Substitution Effect in Value Theory;R G D Allen;Economic Journal,1950