From 991ed92b7e9c37389c282fd0082cc48ea16287d3 Mon Sep 17 00:00:00 2001
From: Marshall Lochbaum <mwlochbaum@gmail.com>
Date: Fri, 31 Jul 2020 23:02:18 -0400
Subject: Depth-1 structural Under implementation

---
 impl.bqn | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/impl.bqn b/impl.bqn
index 558ef06b..2285f66e 100644
--- a/impl.bqn
+++ b/impl.bqn
@@ -416,3 +416,10 @@ _repeat_←{
   (|⊑<⟜0⊑pos‿neg˜)⚇0 n
 }
 ⍟ ↩ _repeat_
+
+_under_←{
+  i←↕×´s←≢𝕩
+  v←⥊𝕨𝔽○𝔾𝕩⋄gi←⥊𝔾s⥊i⋄k←¬i∊gi
+  s⥊(⍋(/k)∾gi)⊏(k/⥊𝕩)∾v
+}
+⌾ ← _under_
-- 
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