Warning
This will be moved to my wiki
An empty program is defined as a program that runs an implementation of the empty algorithm. The empty algorithm does literally nothing.
A program is considered an "instance" of TEP if and only if it does nothing. There are 3 sets/categories an instance may belong to:
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Identity to The Empty Program is defined in terms of payload size. A program is identical iff the payload of its "container" is absolutely empty. This container can be (but it's not limited to) a text file, a raster image file, an audio file, chemical bonds, etc. An example of identity is a 0x0 pixel image interpreted using a programming language in which pixels are "OpCodes" (like in Piet). If a program is identical to TEP, it's considered "pure".
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Equality is defined in terms of payload content. If a program has no instructions to execute, but it has compiler or interpreter directives (or anything akin to directives), it's considered equal. An example is a program that imports a library, then proceeds to do nothing. Another example is a program that activates "strict mode" then does nothing.
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Equivalence is defined in terms of actions, effects, and output. If a program has instructions, but these instructions do not affect the environment in a meaningful way, and/or the program doesn't output any data, it may be considered equivalent. An example is a program that loops 4 times but halts and does nothing else. Another example is a program entirely composed of "No-Ops" (operators, functions, and/or subroutines that do nothing but waste time).
The set of identical programs is a subset of the equal programs. The set of equal programs is a subset of equivalent ones.
Programs outside all these 3 sets are not EPs. However, a program may belong to one of these sets depending on how it's interpreted, which depends on both the chosen (arbitrarily) programming lang and its implementation of it. Source code comments are kind of controversial, because in some langs (like JS) they can have a subtle impact in the runtime of a program and its interaction with other components, even when eval isn't involved.
Any identical and/or equal program has a time (and energy) complexity of O(0), and only identical programs have space complexity of O(0). Any other equivalent program has O(1) for the reasons mentioned above. More info on SO
This program is a polyglot in a lot of langs. But it's also a true polyglot in the sense that it does exactly the same thing in many langs.
It can also be considered a trivial quine, but since the program doesn't make use of I-O, it doesn't output an empty string, it outputs an undefined value, which is not quite the same.
The code coverage is either undefined, 0%, 100%, or Infinity% lol