law: Patents Act, 1970
  11. Priority dates of claims of a complete specification
  (1) There shall be a priority date for each claim of a complete
  
  specification.
  (2) Where a complete specification is filed in pursuance of a
  
  single application accompanied by-
  (a) a provisional specification; or
  (b) a specification which is treated by virtue
  
  of a direction under sub-section (3) of section 9 as a provisional
  
  specification, and the claim is fairly based on the matter disclosed in the
  
  specification referred to in clause (a) or clause (b), the priority date of
  
  that claim shall be the date of the filing of the relevant specification.
  (3) Where the complete specification is filed or proceeded with
  
  in pursuance of two or more applications accompanied by such specifications as
  
  are mentioned in sub-section (2) and the claim is fairly based on the matter
  
  disclosed-
  (a) in one of those specifications, the
  
  priority date of that claim shall be the date of filing of the application
  
  accompanied by that specification;
  (b) partly in one and partly in another, the
  
  priority date of that claim shall be the date of the filing of the application
  
  accompanied by the specification of the later date.
  (4) Where the complete specification has been filed in pursuance
  
  of a further application made by virtue of sub-section (1) of section 16 and
  
  the claim is fairly based on the matter disclosed in any of the earlier
  
  specifications, provisional or complete, as the case may be, the priority date
  
  of that claim shall be the date of the filing of that specification in which
  
  the matter was first disclosed.
  (5) Where, under the foregoing provisions of this section, any
  
  claim of a complete specification would, but for the provisions of that
  
  sub-section, have two or more priority dates, the priority date of that claim
  
  shall be the earlier or earliest of those dates.
  (6) In any case to which sub-sections (2), (3), (4) and (5) do
  
  not apply, the priority date of a claim shall, subject to the provisions of
  
  section 137, be the date of filing of the complete specification.
  (7) The reference to the date of the filing of the application
  
  or of the complete specification in this section shall, in cases where there
  
  has been a post-dating under section 9 or section 17 or, as the case may be, an
  
  ante-dating under section 16, be a reference to the date as so post-dated or
  
  ante-dated.
  (8) A claim in a complete specification of a patent shall not be
  
  invalid by reason only of-
  (a) the publication or use of the invention so
  
  far as claimed in that claim on or after the priority date of such claim; or
  (b) the grant of another patent which claims
  
  the invention, so far as claimed in the first mentioned claim, in a claim of
  
  the same or a later priority date.