Function tempered_observe 

pub fn tempered_observe<T: SampleType>(
    addr: Address,
    dist: impl Distribution<T> + 'static,
    value: T,
    beta: f64,
) -> Model<()>

A tempered observation: at β = 1 this is exactly observe(addr, dist, value) (the log-density lands in log_likelihood); at other β it is factor(β · log p(value)) (landing in log_factors). Both accumulators are tempered together by fugue’s SMC, so the two forms are interchangeable under tempering — the β = 1 form is preferred because it keeps the likelihood/prior decomposition visible in the trace.