Function prepare 

pub fn prepare<X: ReferenceXml, W: Work>(
    access: &Access<'_, X, W>,
    bound: &Bound<X::Id, X::Document, X::Generation>,
    signed: &Reading<X>,
    index: usize,
) -> Result<Prepared<X>, AssociationError<X::Error, X::Id>>

Reads and associates a commitment through the same two kernels used by individual queries. Partial reference results are never returned on refusal.