Combinatorial background for non-structure

This was supposed to be an appendix to the book "Non-structure", and probably will be if it materializes. It presents relevant material, sometimes new, which was used in works which were supposed to be part of that book. In section 1 we deal with partition theorems on trees with omega levels; it is self contained. In section 2 we deal with linear orders which are countable union of scattered ones with unary predicated, it is self contained. In section 3 we deal mainly with pcf theory but just quote. In section 4, on normal ideals, we repeat [Sh:247]. This is used in [Sh:331].