In spreadsheets, formulas are typically propagated by copy & paste, generating numerous instances of the same formula throughout the spreadsheet. The resulting update dependencies make it hard to modify the formula in a consistent way [ESPECIALLY WEAKLY STRUCTURED PROBLEMS, TRIAL & ERROR]. To mitigate the problem, it is suggested to abstract away from the individual formula and employ what could be conceived as "formula classes" , where the structure of the formula is maintained at a single point of definition.