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1-- Yes, perfectly fine (I can’t recall what this structure is called, though. It looks like half of a correlative comparison-- the sooner the better, etc).
If you miss the last train, it will be all the worse for you.
Why do you have such big eyes, Grandma?-- The better to see you with, Little Red Riding Hood.
2-- Themselves is in italics for stress. Rosten may have done it himself, or it may have been italicized by the editor of your source.
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“1- Which shirt do you like better?” is the correct of the two. (Your second sentence is not OK.)
In your original sentence and also in MM’s Little Red Riding Hood sentence, “the better” also has the sense of “in order to (do something better/more easily)”
Why do you want to wear that shirt? The better to keep cool.
You could say: “Which shirt is the better of the two?”
That would just mean “Which shirt is the better one of the two shirts”
In the sentence “If you miss the last train, it will be all the worse for you.” the words all the are idiomatic when used together this way and mean even.
Have my added explanations confused you all the more? :shock: :lol: