"Legally" are a tricky word when it comes to patent lawsuit. The...

"Legally" are a tricky word when it comes to patent lawsuit. The process of proving someone infringing your patent are technical, time consuming and exorbitantly costly.

Example (in layman's term), Mr A patented driving method to work from point A to point B by building a straight road connecting it. Mr B patented his method by building a road that arch from point A to point B. Both methods will reach the same destination. So, how are you going to solve this problem? (Sileach anyone? )

Failing to prove someone infringes your patent can lead to the demise of a company financially, so there for, a patent are usually obtained to protect your own company more than using it to litigate other company into submission (hence the term Patent troll).