Solution (source code)

= Solution

An <estimator> $T$ of a parameter or estimand $g(\theta)$ is an <unbiased estimator> if its <expectation> exists and
$$
\boxed{\mathbb E_\theta[T]=g(\theta)\quad\text{for every admissible }\theta}.
$$
Unbiasedness concerns the sampling mean of the <estimator> over repetitions, rather than equality to the target for any particular observed sample.