During the development of Improv, the Lotus team discovered that these sorts of formulas were both difficult to use, and resistant to future changes in the spreadsheet layout. Their solution was to make the user explicitly define the semantic content of the sheets—that the B column contained "cars sold". These data ranges were known as "categories". Formulas were written by referring to these categories by name, creating a new category that could be (if desired) placed in the sheet for display. Using the car example, the formula in Improv would be codice_3. Changes to the layout of the sheet would not affect the formulas; the data remains defined no matter where it is moved. It also meant that formulas calculating intermediate values did not have to be placed in the sheet and normally did not take up room. The downside to Improv's approach is that it demanded more information from the user up-front, and was considered less suitable for "quick and dirty" calculations or basic list building.