Function same_value 

pub fn same_value(a: f64, b: f64, epsilon: Option<f64>) -> bool

IfcSameValue: are two reals equal within epsilon?

The schema writes this as (v1 + eps > v2) AND (v1 < v2 + eps), which is an exclusive band: values exactly epsilon apart are NOT equal. A symmetric (a - b).abs() <= eps would accept that boundary, so the strict comparison is kept deliberately.

None selects the schema default of 1e-6, matching EXPRESS NVL.