Initializes the dict in the base class and also creates an auxiliary dictionary (I used a defaultdict) named _rdict (reversedict: you must use this name for the bsc to work correctly) whose key(s) (the values in the bidict) are associated with a set of values (their keys in the bidict): initialize _rdict by iterating through the newly initialized dictionary

In a unit cell of fcc structure, indicate the position of one of the tetrahedral interstitial sites by plotting the corresponding tetrahedron. do the same for one of the octahedral interstitial sites (in a separate fcc unit cell). mark the positions of all the tetrahedral and octahedral interstitial sites in the unit cells. how many equivalent tetrahedral sites and how many equivalent octahedral sites are contained in a fcc unit cell, respectively. what is the coordination number for a tetrahedral site and what is the coordination number for an octahedral site?