“…However, the short rate, defined as the beginning of the term structure of interest rates, is only a theoretical variable, not observed on the market. In practice, it can be approximated by a yield with short maturity, such as overnight in [5], [6], [8] or 1-month yields in [2], [3], etc. Using 1-month (or some other) yields is, however, not consistent with the interpretation of the short rate as limit of the yields, as maturity approaches zero.…”