. eight types / doors of pervasion, the eight approaches of pervasion. A logical relationship, in which, the eight requirements of congruency for two things are mutually inclusive: 1) if it is "x" it is "y"; 2) if it is "y" it is "x", yin khyab gnyis; 3) if it is not "x" it is not "y"; 4) if it is not "y" it is not "x", min khyab gnyis; 5) if there is "x" there is "x"; 6) if there is "y" there is "x", yod khyab gnyis; 7) if there is no "x" there is no "y"; 8) if there is no "y" there is no "x", med khyab gnyis