List of Footnotes

1 It should be noticed that the optical bench design shown in Figure 4* is one the earlier ones proposed for the LISA mission, and it represents one of the possible configurations for integrating the onboard drag-free system with the TDI measurements. Although other optical bench designs will result into different inter-proof-mass phase measurements, they can be accommodated within TDI [37].
2 A module is an Abelian group over a ring as contrasted with a vector space which is an Abelian group over a field. The scalars form a ring and just like in a vector space, scalar multiplication is defined. However, in a ring the multiplicative inverses do not exist in general for the elements, which makes all the difference!