جاءني زيد لا عمرو
Zayd came to me, not ʿAmr.
The coordinating lā (لا) excludes ʿAmr from the reported coming while leaving Zayd within it. “Zayd came, not ʿAmr” is materially different from a sentence using wāw, which includes both.
The form is particularly useful when the hearer has mistakenly included ʿAmr or is likely to assume his participation. The short contrasting phrase corrects that expectation.
The negation concerns ʿAmr's participation in this predicate, not his existence or all possible actions. The scope of the correction must remain local to the assertion.