Day 12 shorter.

p12.dyalog

@@ -1,7 +1,7 @@
 ⎕IO←0 ⋄ ⎕PP←17
 s←15↓⊃p←'#'=⊃⎕NGET'p12.txt'1 ⍝ initial state
-u←↑5↑¨2↓p ⋄ v←⊃∘⌽¨2↓p ⍝ patterns and replacements
-f←{v[u⍳⍉0 ¯1↓(5,5+≢⍵)⍴0 0 0 0,⍵]} ⍝ next generation
+u←5↑¨2↓p ⋄ v←⊃∘⌽¨2↓p ⍝ patterns and replacements
+f←{v[u⍳5,/4⌽⍵,⍨8/0]} ⍝ next generation
 g←{+/(⍸⍵)-0.5×(≢⍵)-≢s} ⍝ score function
 g f⍣20⊢s ⍝ part 1
 t←f⍣{≡/(⊢-⌊/)∘⍸¨⍺⍵}s ⍝ iterate until pattern stabilises