Section 31-A. Participation by school district public libraries

a. A
  school district public library, by resolution  legally  adopted  by  its
  board  of  trustees, may elect to become a participating employer in the
  retirement system, separate  and  distinct  from  the  school  district.
  Acceptance  of  the  school  district  public library as a participating
  employer  in  the  retirement  system  shall  be  mandatory   with   the
  comptroller.
    b.  The  officers and employees of such library shall be credited with
  such periods of prior service as shall be certified by the  library  for
  service  rendered  to  it,  or  its predecessor, or the state, or in any
  other capacity approved by such library and the comptroller. Service for
  such library after the date on which it commences to participate in  the
  retirement  system  shall be considered as member service. An officer or
  employee of such library who, as of the  date  he  is  so  approved  for
  membership  in the retirement system, is already a member thereof, shall
  not have his total credit reduced by such approval. Any reserve held  on
  account of any such officer or employee in the pension accumulation fund
  shall  be  used as an offset against the deficiency contribution payable
  thereafter by such library on account of such officer  or  employee  for
  any prior service credit and any such previous credit.