pub trait NutationCalculator {
// Required methods
fn nutation_iau2000a(&self) -> TimeResult<NutationResult>;
fn nutation_iau2000b(&self) -> TimeResult<NutationResult>;
fn nutation_iau2006a(&self) -> TimeResult<NutationResult>;
// Provided method
fn nutation(&self) -> TimeResult<NutationResult> { ... }
}