⇄ — Inverse pairf⇄g calls f; its inverse is g⇄f.
f←{⍵+1}⇄{⍵-1} ⋄ f 5 ⍝ 6
f←{⍵+1}⇄{⍵-1} ⋄ f⍣¯2⊢5 ⍝ 3
Dyadic inversion holds X fixed: X g (X f Y) must recover Y.
f←{⍺+⍵}⇄{⍵-⍺} ⋄ 3(f⍣¯1)8 ⍝ 5
f←{⍺+⍵}⇄{⍵-⍺} ⋄ (3∘f)⍣¯1⊢8 ⍝ 5
Left binding preserves the pair. For right binding, pair the bound monad: (f∘A)⇄undo.