P₁      ← ↥∩=₃⟜+⊸(/+⬚0↻⊂A₂C₂)
Corners ← °⊚×99⋯⇡4
P₂      ← ↥Corners P₁
P!      ← /+♭⍥₁₀₀^
⊃P!P₁P!P₂&rl(=@#)&fo"i/18.in"

~/aoc15ua/18