Notions around tree property 1

In this paper, we study the notions related to tree property 1 (=TP1), or, equivalently, SOP2. Among others, we supply a type-counting criterion for TP1 and show the equivalence of TP1 and k - TP1. Then we introduce the notions of weak k - TP1 for k ≥ 2 , and also supply type-counting criteria for those. We do not know whether weak k - TP1 implies TP1, but at least we prove that each weak k - TP1 implies SOP1. Our generalization of the tree-indiscernibility results in Džamonja and Shelah (2004)[5] is crucially used throughout the paper.