Suppose I have a grammar such that there exist $n$ production rules which contain only terminal symbols, and none of these rules produce the same terminal (disjoint).
$A ::= x|y|z$
$B ::= a|b|c$
$N ::= l|m|k$
Further suppose that I cannot simply merge these production rules together as they are used in different parts of the grammar.
How can I hence determine or rather choose, the start non-terminal $S$, for purposes of $LL(1)$ parsing?