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Programming is divided into three major categories with increasing complexity of reasoning in program validation: sequential programming, multiprogramming, and real-time programming. By adhering to a strict programming discipline and by using a suitable high-level language molded after this discipline, the complexity of reasoning about concurrency and execution time constraints may be drastically reduced. This may be the only practical way to make real-time systems analytically verifiable and ultimately reliable. A possible discipline is outlined and expressed in terms of the language Modula.
Niklaus Wirth (1977) studied this question.