Resources for learning poset isomorphism proofs

[PCSL]

I'm curious if there is a site like Paul's Online Notes for abstract algebra classes on set theory, functions, etc.

Lately I've been having trouble with isomorphisms of posets, so if there is a resource where I could view some proofs of theorems relating to isomorphisms of posets that would be awesome.

Thanks for any help you can offer, my textbook is fine - I'd just like some more practice.

 

[PCSL]

I found a site called proofwiki but it did not have many proofs (seemed like it was a startup). Maybe you guys know of some larger databases of proofs?

 

[PCSL]

This will be the last time I'll bump this.