If *L*_{1}, *L*_{2} {0,1}*, and
, then
*L*_{2} P implies *L*_{1} P.

For any instance of *L*_{1}

map to *L*_{2} (poly time)

solve *L*_{2} (poly time)

Thus if we can solve *L*_{2} in poly time we can solve *L*_{1} in poly time.