Naked & hidden quads
Medium
The four-cell extension of pairs and triples: four cells limited to the same four letters (or four letters limited to the same four cells) lock those letters and cells together, ruling out the rest of the unit.
Medium
The four-cell extension of pairs and triples: four cells limited to the same four letters (or four letters limited to the same four cells) lock those letters and cells together, ruling out the rest of the unit.