pub fn observe_into(&self, challenger: &mut SC::Challenger) {
        challenger.observe(self.commit.clone());
        challenger.observe(self.pc_start);
        challenger.observe_slice(&self.initial_global_cumulative_sum.0.x.0);
        challenger.observe_slice(&self.initial_global_cumulative_sum.0.y.0);
        // Observe the padding.
        challenger.observe(Val::<SC>::zero());
    }
Observes the values of the verifying key into the challenger.
crates/stark/src/machine.rs