"Write the program that prints its own source code"
See the catalog at Puzzles/Quine
In J that would be "write an expression which results in a string that is composed of same characters in same sequence as original expression.
Another way to say it is to define string s such that (-: ".)s
It can be debated whether empty string counts as J expression and therefore is allowable entry, so to reduce on trivial discussion let's assume non-empty s.
Here is a solutions
And another one:
And this one has same length (24 characters) now but may be reduced to 22 in (future) J6
Can there be shorter expressions with this property?
Is it possible to construct expression with this property that has odd number of characters?