st: how to search every observation of one variable in another variable

[ibrahim bostan <ibrahimbstn@gmail.com>]

 I have a dataset which have id number of patents applied by a firm and
 the id number of patents cited by this patent. I am trying to have an
 indicator, as below shown, which will equal one if patent applied by
 the firm is citing a patent which is applied by the same firm.



 cited pt_no   citing_pt_no      patent owner            indicator
 10              20                      a                       0
 11              21                      a                       0
 21              22                      a                       1
 20              23                      a                       1
 20              24                      b                       0
 24              25                      b                       1
 25              26                      b                       1
 1               27                      c                       0
 3               28                      c                       0
 5               29                      c                       0

thanks
 ibrahim
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