About EasterMonster:

coloin wrote:It is easy to find two wrong clues which scupper the "puzzle" by very simple techniques.

For one false clue (= simple or depth 1 T&E), any one I've tried required many steps before leading to a contradiction or it led to nothing. Moreover, even with three false clues that led to the assertion of a strong nrczt-backdoor, the final path to the solution remained complex.

I have no opinion on two wrong clues (= depth 2 T&E) leading to an easy contradiction and an easy solution. Can you give the two clues? It seems very likely there are 2 such clues for the contradiction part. But what I don't see is why you say it is easy to find them and then why this would lead to an easy solution. Related question: when we know the two clues together lead to a contradiction, how easy is it to decide which may be eliminated?

coloin wrote:Sudoku Explainer finds and rates assumptive solution paths.

Here I say Sudoku Explainer is making a big mountain out of a molehill, maybe you can confirm this

T&E is a whole family of algorithms (see the "concept of a resolution rule" thread), depending on which set of rules is used to prune the search.

AFAIK, SE uses T&E pruned by a lot of logic rules.

I think Champagne's algorithm works the same way: breadth-first search (instead of the usual depth-first) pruned by a lot of logic rules, with the assumptive part disguised under tagging, layers, fusion of layers, choice and all the algorithmic glue.

In this context, the rate of a puzzle is highly dependent on the rules used to prune the search. Based on Ruud's top 10,000, I've shown that nrczt rules completely change the rating landscape.

The most stupid rating would certainly be the computation time of an algorithm, especially one relying on massive T&E or tagging, for which humans and computers do not perform the same way. SE is smarter than this, as its ratings rely on the most complex rule needed to solve the puzzle. But, for levels where logic rules are not enough and some form of T&E is used, the rating is very unclear to me. Indeed, I don't understand at all what "dynamic forcing chain" means.

In the reference you're mentioning, you say "A re-look at the puzzle [EM] does show that the 3@r4c1 can be inserted with ultra-simple techniques",

but you don't say which ultra-simple techniques you're thinking of. (You may have said it before in the same thread, but I haven't read its 53 pages).