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"eval", followed by whatever chars are required to get a string.

I think you mean "the minimum to get a Turing Machine", which is not the same. But I am being pedantic. Very, very pedantic. As befits the topic. :)

But what's in that string? That still counts. What I should have done was put an additional restriction on what IO is available. Otherwise, something like "eval `cat f`" or something could be all powerful.

My first attempt shows Ruby simulating a cyclic tag system with only 15 unique characters including newlines and spaces: https://github.com/elitheeli/oddities/raw/master/only_a_few_...

EDIT: down to 14 characters.

"But what's in that string? That still counts."

Sure, but it counts regardless of what you're talking about. We don't generally talk about charging data against the TM because they all need data of some sort to do anything interesting. "eval" still gets you there. (Pedantic.)

I should have phrased as "what is the minimum number of characters that need to be seen by a Ruby parser in order to have something Turing equivalent to Ruby without a limited character set?"

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