Porting APL Sudoku solver(s) about learn-bqn HOT 2 CLOSED

Box ← {>𝕩/<˘𝕩‿∘⥊𝕩/1+↕𝕩⋆2}
# (1+↕4‿4) ∾¨ Box 2
Rcb ← {(1+↕𝕩)∾¨Box ⊑0.5⋆˜𝕩}
# Rcb 4‿4
Cmap ← {<˘˘1 (⊑∊)¨ =⌜˜𝕩}
Cmap Rcb 4‿4

Avl ← {(1+↕⊑≢𝕩)(¬∘∊/⊣)(0⊸≠)⊸/⥊𝕩×𝕨⊑Cmap Rcb ≢𝕩}

Avl ← {0≠𝕨⊑𝕩? ⋈𝕨⊑𝕩; (1+↕⊑≢𝕩)(¬∘∊/⊣)(0⊸≠)⊸/⥊𝕩×𝕨⊑Cmap RCB ≢𝕩}

Nxt  ← {w F x:(𝕨 Avl 𝕩) {𝕨˙⌾(w⊸⊑)𝕩}¨ <𝕩}
Nxtv ← {∾𝕨⊸Nxt¨𝕩}        # use like (<s44)Nxtv´⟨0‿0,0‿1,1‿0⟩

Avl ← {0≠𝕨⊑𝕩? ⋈𝕨⊑𝕩; (1+↕⊑≢𝕩)(¬∘∊/⊣)(0⊸≠)⊸/⥊𝕩×𝕨⊑Cmap RCB ≢𝕩}

(<s44)Nxtv´⥊↕≢s44

Sol ← {
    terminated? answer;    # Is there a way to 'break'?
    𝕊¨ nextstates          # This is depth-first search.
}