b⊥b or ⊥⍨b is the number of trailing 1 bits in boolean vector b .
b←(?1e4⍴2),0,20⍴1 c←∧\⌽b cmpx 'b⊥b' '+/∧\⌽b' '+/c' b⊥b → 3.30E¯4 | 0% ⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕ +/∧\⌽b → 4.76E¯6 | -99% +/c → 1.89E¯6 | -100%