 More subtle behaviour occurs when the matrices formula_65 and formula_66 are not so simple; see, for example, the de Rham curve as an example of a quantum finite state machine acting on the set of all possible finite binary strings.Measure-many automata were introduced by Kondacs and Watrous in 1997.The general framework resembles that of the measure-once automaton, except that instead of there being one projection, at the end, there is a projection, or quantum measurement, performed after each letter is read.