Let R be the set of all roots.

Let R be the set of all sets that are not members of themselves.

Let R be the internal resistance of the coil.

Let R be a unital ring, which is not the trivial ring.

Let R be a simple ring which is not right Artinian.

Let M,N and R be as in the previous section.

Let R be a commutative ring with identity 1.

Let R be an algebra over a field k that is an integral domain.

Let R be the exact reciprocal and the approximation.

Let R be a measure of how good the clustering scheme is.