⌿ — Reduce first

Monadic operator. Keys: Alt-Minus /. Hanzi: 汇 (匯)

f⌿Y reduces the first axis.

+⌿2 3⍴⍳6ₓ           ⍝ [3 5 7]ₓ

S f⌿ Y starts each lane from the whole seed S on the right.

10+⌿3 2⍴⍳6ₓ         ⍝ [16 19]

Identities, ⍠K and errors follow /.