Function cmp_lex 

pub fn cmp_lex(a: &ImplicitPoint, b: &ImplicitPoint) -> Sign

Exact lexicographic total order on points (x, then y, then z), over any mix of Explicit/Lpi/Tpi. Zero ⇔ the two points are EXACTLY coincident — this is the interner’s symbolic vertex-identity test (no float weld). A strict total order: antisymmetric, transitive (proven by property test).