def METHOD_NAME(kernel: str) -> str:
    kernel = kernel.replace("-", "").replace("_", "").lower()
    if kernel not in KERNEL_ESTIMATORS:
        est = "\n".join(sorted(k for k in KERNEL_ESTIMATORS))
        raise ValueError(
            f"kernel is not a known kernel estimator. Must be one of:\n {est}"
        )
    return kernel