def METHOD_NAME(requirements):
    unmet_requirements = set()
    for requirement in requirements:
        try:
            version = importlib.metadata.version(requirement.name)
        except importlib.metadata.PackageNotFoundError:
            unmet_requirements.add(requirement)
            continue
        if not requirement.specifier.contains(version):
            unmet_requirements.add(requirement)
            continue
        if requirement.extras:
            raise NotImplementedError("Optional dependency requirements within plugin dependencies "
                                      "are not supported yet")
    return unmet_requirements