In the second episode of the second season of Elementary, murderous mathematicians shed blood over one of the great unsolved problems in mathematics and computer science, P vs NP. Business interests in the episode are backing mathematicians to solve the problem because it would become a skeleton key to a skeleton key to all computer encryption, basically making encryption obsolete.

Spoiler Alert: The episode ends with Sherlock gazing at the 2/3-done equation one last time, because the NSA has requested all of the work and the main murdering math magician.

Both Person of Interest and Elementary are on CBS and both are set in New York City. Person of Interest also does quite a bit with questions of encryption, privacy, and government surveilance by entities like the NSA. Just see the second episode of the third season, "Nothing To Hide," which is all about the problems of getting your security hacked.

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If done carefully (and not just through stuntcasting), you could conceivably see a storyline develop on Person of Interest where the NSA or some other alphabet organization, or a group within an organization, uses the seized P vs NP research to attempt to crack Harold's encryption on the machine, and maybe even have Root intervene to protect her new god.

Without having them necessarily cross paths, Sherlock and Watson could pick up another side of that storyline; perhaps the research is stolen by one of the competing groups within an agency, and the two detectives are asked to try to find who took the research and where it is, since they were involved in the original case.

But in either case, Bear and Sherlock should have a heart-to-heart.