law: Specific Relief Act, 1963
  26. When instrument may be rectified
  (1) When, through fraud or a mutual mistake of the parties, a
  
  contract or other instrument in writing (not being the articles of association
  
  of a company to which the Companies Act, 1956, applies) does not express their
  
  real intention, then 
  (a) either party or his representative in
  
  interest may institute a suit to have the instrument rectified; or
  (b) the plaintiff may, in any suit in which
  
  any right arising under the instrument is in issue, claim in his pleading that
  
  the instrument be rectified; or
  (c) a defendant in any such suit as is
  
  referred to in clause (b), may, in addition to any other defense open to him,
  
  ask for rectification of the instrument.
  (2) If, in any suit in which a contract or other instrument is
  
  sought to be rectified under sub-section (1), the court finds that the
  
  instrument, through fraud or mistake, does not express the real intention of
  
  the parties, the court may, in its discretion, direct rectification of the
  
  instrument so as to express that intention, so far as this can be done without
  
  prejudice to rights acquired by third persons in good faith and for value.
  (3) A contract in writing may first be rectified, and then if
  
  the party claiming rectification has so prayed in his pleading and the court
  
  thinks fit, may be specifically enforced.
  (4) No relief for the rectification of an instrument shall be
  
  granted to any party under this section unless it has been specifically
  
  claimed:
  PROVIDED that where a party has not claimed any such
  
  relief in his pleading, the court shall, at any stage of the proceeding, allow
  
  him to amend the pleading on such terms as may be just for including such
  
  claim.