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From: "Ev. Drikos" <drikosev@gmail.com>
Newsgroups: comp.compilers
Subject: Re: About finding the start symbol of a grammar
Date: Sat, 22 May 2021 06:52:17 +0300
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On 21/05/2021 13:49, Eduardo Costa wrote:
> While there would exist grammars we could recursively check to find out which
> it's start symbol is (i.e.: it's the only rule that used the rest of them,
> where checking every other resulted in dangling rules that weren't even called
> in), there might be other grammars for which more than one rule yields full
> coverage (all of these obviously defining different languages) and so leading
> to ambiguity.

IMHO, it can be so simple as you describe here without important overhead.
Typically, a parser will reduce the start symbol and finish. All rules
that yield full coverage can be ie alternatives of a single root symbol:

RootSymbol -> R1 | R2 | ... | Rn

Ev. Drikos