In the two earlier chapters on semantics, we have defined the semantics of the compound statements S0; S1, IF, and DO by defining their predicate transformers in terms of the predicate transformers of their constituent statement(s). This raises the following question. What is or could be the relation between the execution of a compound statement and the executions of its constituent statements? Or, a bit more specifically, if we know how to implement the constituent statements, how could we then implement the semicolon, the alternative construct, and the repetition? These are the questions to which this chapter is devoted. We shall deal with the three compound statements in the order in which they have been introduced. (As is only to be expected, this is also the order of increasing complexity.)
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