Use of l-values as operator operands is particularly notable in unary increment and decrement operators. The counters would increment, decrement, or shift in response to internal inputs. Qt uses atomic compare-and-swap operations to increment or decrement the internal reference counter. There are methods to increment (V) and to decrement (P) a private integer codice 20. However, increment and decrement operators are "not" supported. Thompson went further by inventing the increment and decrement operators (codice 8 and codice 9). In QCL, decrement is done by "undoing" increment. The individual heads will move left (for decrement) and right (for increment). The five restricted productions are return, throw, break, continue, and post-increment/decrement. Mackworth's results indicated a decline in signal detection over time, known as a vigilance decrement. Considerable research has been devoted to the reduction of the vigilance decrement. In some cases the vigilance decrement was eliminated or not apparent. Other theories such as "resource diffusion" and "response decrement" are similar to blocking. Widespread pilfering by villagers for firewood and fodder also represents a major decrement. Too much or too little anxiety can lead to performance decrement.