NP Problem and reduction
Since NP-Complete problems can be reduced to each other, If we can reduce a problem to a specific NP-Complete problem. It means that we can reduce it to any NP-Complete problem.
The reason is All problems in NP-Complete can be reduced to SAT and SAT to 3-SAT and 3-SAT to CLIQUE and so forth. So reducing to a problem in NP-Complete means reducing to all problems in NP-Complete.