In the classical case, the invariance, or symmetry, group and the covariance group coincide, but, interestingly enough, they part ways in relativistic physics. The symmetry group of the general theory of relativity includes all differentiable transformations, i.e., all properties of an object are dynamical, in other words there are no absolute objects. The formulations of the general theory of relativity, unlike those of classical mechanics, do not share a standard, i.e., there is no single formulation paired with transformations. As such the covariance group of the general theory of relativity is just the covariance group of every theory.
What are not pair with transformations in the theory of relativity?
single formulation

Since the Balfour Declaration of 1926 and the Statute of Westminster 1931, the all Commonwealth realms have been sovereign kingdoms, the monarch and governors-general acting solely on the advice of the local ministers who generally maintain the support of the legislature and are the ones who secure the passage of bills. They, therefore, are unlikely to advise the sovereign or his or her representative to withhold assent. The power to withhold the royal assent was exercised by Alberta's lieutenant governor, John C. Bowen, in 1937, in respect of three bills passed in the legislature dominated by William Aberhart's Social Credit party. Two bills sought to put banks under the authority of the province, thereby interfering with the federal government's powers. The third, the Accurate News and Information Bill, purported to force newspapers to print government rebuttals to stories to which the provincial cabinet objected. The unconstitutionality of all three bills was later confirmed by the Supreme Court of Canada and by the Judicial Committee of the Privy Council.
What the did Accurate News and Information Bill hope to accomplish?
force newspapers to print government rebuttals to stories to which the provincial cabinet objected

There are several invertebrate species whose brains have been studied intensively because they have properties that make them convenient for experimental work:
Which brains are easier to work on, vertebrates or invertebrates?
invertebrate