Expressions and Their Structure (Ch 33 of Elementary Intro to Wolfram Language)

I am perplexed that a PhD MIT guy from Google would take his time and read w-clan propaganda. What exactly don’t you get? There’s no other programming language other than Wolfram’s that does symbols language computation. Let me put it in your MIT Symbols symbolic languages == { wolfram language, nothing else}

I am particularly perplexed by the following footnote. Can someone explain to me what is meant by this?

> The basic concept of symbolic languages comes directly from work in mathematical logic stretching back to the 1930s and before, but other than in the Wolfram Language it’s been very rare for it to be implemented in practice.