declare namespace isWellKnownSymbol { type WellKnownSymbolName = Exclude< keyof SymbolConstructor, | 'constructor' | 'for' | 'from' | 'keyFor' | 'prototype' >; type WellKnownSymbol = SymbolConstructor[WellKnownSymbolName]; } declare function isWellKnownSymbol(sym: unknown): sym is isWellKnownSymbol.WellKnownSymbol; export = isWellKnownSymbol;