BA2∧A=⌈\BA1×A←+\BA2>¯1↓0,BA2 Groups of ones in BA2 pointed to by BA1 (or trailing parts).
BV2∧A∊(BV1∧BV2)/A←+\BV2>¯1↓0,BV2 Groups of ones in BV2 pointed to by BV1.
⎕IO+(⍴NM)⊤-⎕IO-(,(NM=(⍴NM)⍴⌈⌿NM)∧NM=⍉(⌽⍴NM)⍴⌊/NM)/⍳×/⍴NM Index pairs of saddle points.
(0,⍳(⍴XV)-IS)∘.+IS Moving index of width IS for vector XV.
+/A∧⍉A←NV1∘.≤NV2 Number of ?s intersecting ?s (NV1=starts, NV2=stops).