diff --git a/phase1.dyalog b/phase1.dyalog
index 15c94ba..a81ef5b 100644
--- a/phase1.dyalog
+++ b/phase1.dyalog
@@ -17,4 +17,6 @@
         zigzag←∧/2=∘|2-/∘×2-/(10∘⊥⍣¯1)
         ⍝ 9: Rise and Fall
         risefall←{∧/(⍳∘≢≡⍋)¨(⊂((⊢⍳⌈/)↑⊢),⍵),⊂⌽((⊢⍳⌈/)↓⊢),⍵}
+        ⍝ 10: Stacking It Up
+        stacking←{↑⊃,/↓¨⍕¨⍵}
 :EndNamespace