common law = precedent
It's used in every case
The basic routine for researching a case goes like this:
1--define the crime
2--define the specific section of the US code that has been violated
3--research cases indexed by that code for prior interpretations likely to be used
Step 2 is a research of statutory law.
Step 3 is a research of common law.
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The second answer is wrong.
There's not a single case in any law library in America that references English common law. Courts are restricted to American statutes and American precedent.

