Are there any advanced developers who can answer these questions?
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What are the differences between string, bytes32, byte[], bytes?

Which one do I use, when?
What’s happening when I cast a string to bytes? Can I cast to byte[]?
How much do they cost?
How are mappings stored by the EVM?

Why can’t I delete a mapping?
Can I have mappings of mappings? (Yes, but how does that work?)
Why is there storage mapping, but no memory mapping?
How does a compiled contract look to the EVM?

How is a contract created?
What is a constructor, really?
What is the fallback function?