Instruction sequence processing operators

This paper concerns instruction sequences whose execution involves the processing of instructions by an execution environment that offers a family of services and may yield a Boolean value at termination. We introduce a composition operator for families of services and three operators that have a direct bearing on the processing in question. Together they are simpler and more powerful than the operators proposed for the same purpose in earlier work. Some of the operators allow for terms to be built that are not intended to denote anything. We propose to comply with conventions that exclude the use of such terms