PWO PCI PSI

For the first two weeks, we have done a lot on those Principles( Well-ordering, simple-induction and complete induction). Today's lecture we actually made those principles more clearly about their relationships. Those terms are essentially all the same. One term can be drived from the others. Those proofs are we have done today, is written in textbook as well, so I don't want to repeat here. It is well worthy to read through, an it will make all those concepts are more clearly.