Spatial and temporal patterns in Neolithic and Bronze Age agriculture in Poland based on the stable carbon and nitrogen isotopic composition of cereal grains by Mueller-Bieniek, A, Nowak, M, Styring, A, Lityńska-Zając, M, Moskal-Del Hoyo, M, Sojka, A, Paszko, B, Tunia, K, Bogaard, A