pub trait PrecessionCalculator {
// Required methods
fn precession_iau2000(&self) -> TimeResult<PrecessionResult>;
fn precession_iau2006(&self) -> TimeResult<PrecessionResult>;
// Provided methods
fn precession(&self) -> TimeResult<PrecessionResult> { ... }
fn bias_precession_matrix(&self) -> TimeResult<RotationMatrix3> { ... }
}