Rules of omitting or requiring certain "letters" and "numbers" from the hexadecimal key "string" I mentioned were examples to demonstrate what my experiential finder is capable of. I use various and different patterns and methods of this sort. I change them often, experimenting. That is the reason why I created my version this way, so private key selection can be manipulated based on given "string" criteria.
I needed to choose some criteria by which to manipulate odds and cut down BTC puzzle scanhash times from hundreds of years to something lower, something that can be done in months, weeks, or days, based on given rules, "skip-hash".
Is it rational from a mathematical point of view when speaking about any generic BTC keys?
No, not really at all. Is it ridiculous? Yeah, kind of to some extent, surely. And what?
I really understand everything you mentioned, I get everything. I knew it even before.

I have been programming since the 80s, I have (surprisingly) degrees in mathematics and computer science, and (this is very scary, LOL...) I have been lecturing those for quite some time in the past.
In the late 90s and early 00s, amongst other things, I worked on AAA game titles, programming 3D engines, game physics, logic, and visual renderings in times when it was pretty hardcore and a lot of things needed to be figured out and done "on the knee", not as easy as these days. And many other things related to the field up to this time.
I realize heavy storm clouds can sometimes resemble dragons, or sheep, or something creepy, depending on mood, as it is the way the human brain likes to make associations and tries to find patterns and see things where they are not really. Yes, of course.
Is my experimental Bitcrack version a scientific tool? No, no way. It never was. That was never the intention.
Is it a kind of tool where I can predict, bet, and try searching for private keys, looking at them as "strings" consisting of "numbers" and "letters" and based on given criteria, restrictions, and patterns, where I can experiment with various prediction and probability systems in it? Yes, this is kind of what it is.
Searching for a private key with it is based on luck, as was already told, it can be said "skip-hashing" depending on parameters, my way of picking cherries from a cake approach.
Is it rational? Well, it is my approach, be it rational or not, I still stand by my opinion that it adds effectiveness when searching for BTC puzzle keys. I repeat again - puzzle keys.
As this is what it is about, I do not care about common BTC private keys, generic BTC private keys. I care only about the low-bit BTC puzzle keys.
Yeah, I know they are random too, yes, yes, ... yes, I know that if they were in a different format it would be different.
I had to approach it somehow, so I chose to look at keys as hexadecimal "strings", simply like that, it is nice and appealing to see them as single characters, "numbers" and "letters".
As I already told, I don’t know exactly what BTC puzzle key #67 (the ending part) looks like, but I am pretty sure it doesn’t look like this, for example:
All characters of #67 are "letters"? No. All characters are "numbers"? No.
The first part of the key is only "letters" and the other part is only "numbers"? Or vice versa. No.
It is like exactly "letter-number-letter-number-letter-number..." till the end? No. No way, I would even put my hand in the fire that no. Yes, this approach is about betting on something and holding to it.
Etc.
I made my experimental finder this way basically because already solved puzzle keys are usually published in hexadecimal "string" format, and when I always looked at some already solved BTC puzzle keys, I told myself something like, ahhhhh... I knew that "EE" would be in it, or I thought there would be zero occurrences of "4" anywhere in this one, things like that.
Thus, I made myself a GPU tool exactly for that, so when I want, I can scan a given range fast on my few Nvidia cards using any sort of "string," "letter(s)," or "number(s)" criteria. Such as, I want to scan the given range but omit number "4" anywhere in the "string" I can, I want exactly 2 letters "EE" to be anywhere in it next to each other, I can, I want to have any unknown "letter-letter" anywhere in it, of course, I want to have an occurrence of exactly 5 unknown "letter" in it anywhere, no problem. I want it to skip all private keys containing more than the count 9 of any "letter" anywhere in the string, yes, or at least the count of 3 "number" that has to be lower than <8, sure, things like that, etc.
Any pattern, any sort, operators, conditions, any offset, anywhere, any count.
With this, I test my chances in ways I needed and I test various probability systems and approaches I like, new perspectives I try to figure out, I experiment - it is fun, and I hope for luck.
Anyway, what I wanted to say about it, I already said, speaking about it more again and again now would be going in the cycles round and round.
As I already told you, if I ever solve the low-bit BTC puzzle with it and finally the price will arrive at my BTC wallet without being robbed during cashing out by a bot run by a thief, I will publish it, including the source code.
Till then I will be trying my luck with it.
I am pretty stubborn when I bite into something, be it rational or not, I don't care.
