> I don't see how the logic is compatible
Set operations have a natural analogy to Boolean operations.
And in mathematics and CS and and or are often replaced with * and + notations, especially in pre-LaTeX documents.
That's because the truth tables are the same
0 0 0
1 0 1
0 0 1
1 1 2 (2 is true here)
Arithmetic operators + - * / are also "close" in precedence, associativity and context (see perlop ) and the grouping rules are well known.
Furthermore is comparison with < > => <= obvious here.
Also the duplicity of == and eq for comparison comes handy (same "set object" or same "set elements")
> STRING * 3 to be equivalent to STRING + STRING + STRING.
not sure what you mean set elements are unique, if you refer to power-sets the cross operator x or power ** may be the better choice.