Your comment makes the timeline seem very different from the way I remember it. Yahoo was dominant much earlier than Google, and was one of a handful of big search engines. Google was a relative newcomer at the time, which had the benefit of being way better at search, which is why it eventually dominated the competition.
The halting problem is NP hard, technically speaking, but it's much harder than that - it's uncomputable. I don't think it's common to refer to it as NP-hard because it's confusing.
Right. To be clear: the halting problem is not in the class NP. Any problem in NP can trivially be reduced to the halting problem and so the latter is NP-hard.
I wonder if that was part of the reason that some programming languages use constructs like "if / fi" "do / od" etc.
(Note: After writing the above, I checked with ChatGPT, it claims that the main motivation was to make it unambiguous which which "opening word" a "closing word" belonged to.)
This tracks with an old convention in languages like Pascal, which uses begin / end keywords for all blocks, where people would add "end (* if *)" as a comment to make it more explicit which block is being closed.
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