"I take it that computational processes are both symbolic and formal. They are symbolic because they are defined over representations, and they are formal because they apply to representations, in virtue of (roughly) the syntax of the representations."

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The establishment of formal standards for proofs about programs... and the proposal that the semantics of a programming language may be defined independently of all processors for that language, by establishing standards of rigor for proofs about programs in the language, appears to be novel.

— Robert W. Floyd