code: private boolean isRedundantTransform(CrystalTransform tt) {
  
  		Iterator<CrystalTransform> it = visitedCrystalTransforms.iterator();
  		while (it.hasNext()) {
  			CrystalTransform v = it.next();
  
  			if (tt.isEquivalent(v)) {
  
  				logger.debug("Skipping redundant transformation: "+tt+", equivalent to "+v);
  
  				// there's only 1 possible equivalent partner for each visited matrix
  				// (since the equivalent is its inverse matrix and the inverse matrix is unique)
  				// thus once the partner has been seen, we don't need to check it ever again
  				it.remove();
  
  				return true;
  			}
  		}
  
  		return false;
  	}
docs: Checks whether given transformId/translation is symmetry redundant
  Two transformations are symmetry redundant if their matrices (4d) multiplication gives the identity, i.e.
  if one is the inverse of the other.
  @param tt
  @return