@vzn not a student, this is part of some learning I have been doing. Yeah, I tried to have a small example to understand the operators, but it turns out that the only example in the book , is really complex and incomplete, so ill never know how to work backwards from the final answer the autihors have given. It would really help, if you knew of other books./references.

@vzn I tried looking in standard books such as Wolfgang Thomas's Applied Automata Theory, but there isnt any mention of these operators. And no, they are not modern, they have been around for long time, perhaps 1960s.

@GermanShepherd en.wikipedia.org/wiki/Graph_homomorphism

@vzn Im afraid its not the same thing.

@GermanShepherd yes ofc but suspect if you understand graph homomorphism it will help you with tree homomorphism. trees are a subset of graphs.