 Note that they refer to the triplet \(\Omega \subset \Eta \subset \Omega^*\) as a rigged Hilbert space. In the terminology introduced above, they refer in effect to the Gelfand triplet \((\Omega , \Eta , \Omega^x )\) or (equivalently) the associated rigged Hilbert space \((\Omega , \Omega^x)\) .