diff --git a/2023/ruby/day_13.rb b/2023/ruby/day_13.rb
index 7a90360..093da3e 100644
--- a/2023/ruby/day_13.rb
+++ b/2023/ruby/day_13.rb
@@ -1,14 +1,79 @@
-patterns = ARGF.read.split("\n\n")
-  .map { _1.split("\n").map(&:chars) }
-
-def find_fold(pattern)
-  (0.5...pattern.length-0.5).step(1).find {|fold|
+def reflection_points(pattern)
+  (0.5...pattern.length-0.5).step(1).filter_map {|fold|
     a = pattern[0..fold.floor]
     b = pattern[fold.ceil..]
-    a.reverse.zip(b).reject { _1.any?(&:nil?) }.all? { _1 == _2 }
-  }&.ceil
+    if a.reverse.zip(b).reject { _1.any?(&:nil?) }.all? { _1 == _2 }
+      fold
+    else
+      nil
+    end
+  }.map(&:ceil)
 end
 
-verts = patterns.map { find_fold(_1.transpose) }.compact
-hors = patterns.map { find_fold(_1) }.compact
-p verts.sum + hors.sum { _1 * 100 }
+Pattern = Data.define(:pattern) do
+  def reflection_axes
+    ary = to_a
+    reflection_points(ary).map { [:y, _1] } + reflection_points(ary.transpose).map { [:x, _1] }
+  end
+
+  def smudges
+    return enum_for(__method__) unless block_given?
+
+    max_y, max_x = extents
+    (0..max_y).each do |y|
+      (0..max_x).each do |x|
+        smudged = case pattern[[y,x]]
+                  when ?# then ?.
+                  when ?. then ?#
+                  else fail
+                  end
+        yield Pattern.new(pattern.merge({[y,x] => smudged}))
+      end
+    end
+  end
+
+  def to_a
+    max_y, max_x = extents
+    (0..max_y).map {|y|
+      (0..max_x).map {|x|
+        pattern.fetch([y,x])
+      }
+    }
+  end
+
+  def to_s
+    to_a.map(&:join).join("\n")
+  end
+
+  def extents
+    max_y = pattern.keys.map(&:first).max
+    max_x = pattern.keys.map(&:last).max
+    [max_y, max_x]
+  end
+end
+
+patterns = ARGF.read.strip.split("\n\n")
+  .map {|pattern|
+    pattern.split("\n").map(&:chars)
+      .each.with_index.inject({}) {|h, (row, y)|
+        h.merge(row.each.with_index.to_h {|elem,x| [[y,x], elem]})
+      }
+  }.map { Pattern.new(_1) }
+
+# part one
+x, y = patterns.map { _1.reflection_axes.fetch(0) }
+  .partition {|axis,_| axis == :x }
+  .map { _1.map(&:last) } # keep index (discard axis)
+p x.sum + y.sum { _1 * 100 }
+
+# part two
+
+x, y = patterns.map {|pattern|
+  original_reflection_axis = pattern.reflection_axes.fetch(0)
+  pattern.smudges.lazy
+    .flat_map { _1.reflection_axes}
+    .reject { _1 == original_reflection_axis }
+    .first
+}.partition {|axis,_| axis == :x }
+  .map { _1.map(&:last) } # keep index (discard axis)
+p x.sum + y.sum { _1 * 100 }