This site describes solve-engine as it is on main: 2.43.0, which npm does not have yet. npm installs 2.40.0, so a page may show an answer that version does not give yet.
SYMBOLIC_PACKAGE
const SYMBOLIC_PACKAGE: IEnginePackage;Defined in: packages/engine/src/packages/symbolic/SymbolicPackage.ts:187
Symbolic algebra verbs: multiplying out, and (in later phases) factoring, solving and calculus.
The algebra itself lives in symbolic/, which is pure mathematics over the
expression tree. This package is only the grammar surface: which words become
which tokens, and which parselet emits which builtin call.
None of these words is a bare keywordMap entry. See
normalizer/SymbolicCallNormalizerRule.ts for why that matters.