# Richard Stallman

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**Richard Matthew Stallman**, founder of the GNU Project, was an early adopter of APL, and used it to write a text editor as a high school student in the summer of 1969^{[1]}. The same year, he also wrote a now famous rhyme:

Rho, rho, rho of X

Always equals 1

Rho is dimension, rho rho rank.

APL is fun!

This plays on the fact that `⍴X`

gives the shape (length of each axis; "dimension") of `X`

while `⍴⍴X`

gives the rank (number of axes/dimensions) and since the number of axes is always a count, it is a single number, which has the shape `1`

if a vector, and `⍴`

always returns a vector:

```
⎕←X←3 1 4∘.+2 7 1 8
5 10 4 11
3 8 2 9
6 11 5 12
⍴X
3 4
⍴⍴X
2
⍴⍴⍴X
1
```

## References

- ↑ Stallman, Richard M. "RMS Berättar".