diff --git a/Gemfile b/Gemfile
index 52bf0ab..d0c1b96 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,3 +1,4 @@
 source "https://rubygems.org"
 
 gem "minitest"
+gem "pry"
diff --git a/Gemfile.lock b/Gemfile.lock
index df3e92e..6f0338c 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,13 +1,21 @@
 GEM
   remote: https://rubygems.org/
   specs:
+    coderay (1.1.0)
+    method_source (0.8.2)
     minitest (5.8.3)
+    pry (0.10.3)
+      coderay (~> 1.1.0)
+      method_source (~> 0.8.1)
+      slop (~> 3.4)
+    slop (3.6.0)
 
 PLATFORMS
   ruby
 
 DEPENDENCIES
   minitest
+  pry
 
 BUNDLED WITH
    1.10.6
diff --git a/day_07.rb b/day_07.rb
new file mode 100644
index 0000000..edab2d6
--- /dev/null
+++ b/day_07.rb
@@ -0,0 +1,381 @@
+BINDING = Hash.new {|h,k| h[k] = Expr.new(nil, [k], k) }
+MEMOIZED = {}
+
+class Expr < Struct.new(*%i[ op inputs output ])
+  def reduced
+    return MEMOIZED[output] if MEMOIZED[output]
+
+    result = case op
+             when nil
+               input = inputs[0]
+               (input =~ /^\d+$/) ? input.to_i : BINDING[input].reduced
+             when "NOT"
+               ~reduced_inputs[0] % 65536
+             when "OR"
+               reduced_inputs[0] | reduced_inputs[1]
+             when "AND"
+               reduced_inputs[0] & reduced_inputs[1]
+             when "RSHIFT"
+               reduced_inputs[0] >> reduced_inputs[1]
+             when "LSHIFT"
+               reduced_inputs[0] << reduced_inputs[1]
+             else
+               fail "WTF? #{op}"
+             end
+    MEMOIZED[output] = result
+  end
+
+  def reduced_inputs
+    inputs.map {|input| BINDING[input].reduced }
+  end
+end
+
+DATA.read.scan(/(.+) -> (.+)/) do |input, output|
+  inputs = input.split(" ")
+  op = inputs[-2]
+  inputs.delete(op)
+  BINDING[output] = Expr.new(op, inputs, output)
+end
+
+puts BINDING["a"].reduced
+
+__END__
+NOT dq -> dr
+kg OR kf -> kh
+ep OR eo -> eq
+44430 -> b
+NOT gs -> gt
+dd OR do -> dp
+eg AND ei -> ej
+y AND ae -> ag
+jx AND jz -> ka
+lf RSHIFT 2 -> lg
+z AND aa -> ac
+dy AND ej -> el
+bj OR bi -> bk
+kk RSHIFT 3 -> km
+NOT cn -> co
+gn AND gp -> gq
+cq AND cs -> ct
+eo LSHIFT 15 -> es
+lg OR lm -> ln
+dy OR ej -> ek
+NOT di -> dj
+1 AND fi -> fj
+kf LSHIFT 15 -> kj
+NOT jy -> jz
+NOT ft -> fu
+fs AND fu -> fv
+NOT hr -> hs
+ck OR cl -> cm
+jp RSHIFT 5 -> js
+iv OR jb -> jc
+is OR it -> iu
+ld OR le -> lf
+NOT fc -> fd
+NOT dm -> dn
+bn OR by -> bz
+aj AND al -> am
+cd LSHIFT 15 -> ch
+jp AND ka -> kc
+ci OR ct -> cu
+gv AND gx -> gy
+de AND dk -> dm
+x RSHIFT 5 -> aa
+et RSHIFT 2 -> eu
+x RSHIFT 1 -> aq
+ia OR ig -> ih
+bk LSHIFT 1 -> ce
+y OR ae -> af
+NOT ca -> cb
+e AND f -> h
+ia AND ig -> ii
+ck AND cl -> cn
+NOT jh -> ji
+z OR aa -> ab
+1 AND en -> eo
+ib AND ic -> ie
+NOT eh -> ei
+iy AND ja -> jb
+NOT bb -> bc
+ha OR gz -> hb
+1 AND cx -> cy
+NOT ax -> ay
+ev OR ew -> ex
+bn RSHIFT 2 -> bo
+er OR es -> et
+eu OR fa -> fb
+jp OR ka -> kb
+ea AND eb -> ed
+k AND m -> n
+et RSHIFT 3 -> ev
+et RSHIFT 5 -> ew
+hz RSHIFT 1 -> is
+ki OR kj -> kk
+NOT h -> i
+lv LSHIFT 15 -> lz
+as RSHIFT 1 -> bl
+hu LSHIFT 15 -> hy
+iw AND ix -> iz
+lf RSHIFT 1 -> ly
+fp OR fv -> fw
+1 AND am -> an
+ap LSHIFT 1 -> bj
+u LSHIFT 1 -> ao
+b RSHIFT 5 -> f
+jq AND jw -> jy
+iu RSHIFT 3 -> iw
+ih AND ij -> ik
+NOT iz -> ja
+de OR dk -> dl
+iu OR jf -> jg
+as AND bd -> bf
+b RSHIFT 3 -> e
+jq OR jw -> jx
+iv AND jb -> jd
+cg OR ch -> ci
+iu AND jf -> jh
+lx -> a
+1 AND cc -> cd
+ly OR lz -> ma
+NOT el -> em
+1 AND bh -> bi
+fb AND fd -> fe
+lf OR lq -> lr
+bn RSHIFT 3 -> bp
+bn AND by -> ca
+af AND ah -> ai
+cf LSHIFT 1 -> cz
+dw OR dx -> dy
+gj AND gu -> gw
+jg AND ji -> jj
+jr OR js -> jt
+bl OR bm -> bn
+gj RSHIFT 2 -> gk
+cj OR cp -> cq
+gj OR gu -> gv
+b OR n -> o
+o AND q -> r
+bi LSHIFT 15 -> bm
+dy RSHIFT 1 -> er
+cu AND cw -> cx
+iw OR ix -> iy
+hc OR hd -> he
+0 -> c
+db OR dc -> dd
+kk RSHIFT 2 -> kl
+eq LSHIFT 1 -> fk
+dz OR ef -> eg
+NOT ed -> ee
+lw OR lv -> lx
+fw AND fy -> fz
+dz AND ef -> eh
+jp RSHIFT 3 -> jr
+lg AND lm -> lo
+ci RSHIFT 2 -> cj
+be AND bg -> bh
+lc LSHIFT 1 -> lw
+hm AND ho -> hp
+jr AND js -> ju
+1 AND io -> ip
+cm AND co -> cp
+ib OR ic -> id
+NOT bf -> bg
+fo RSHIFT 5 -> fr
+ip LSHIFT 15 -> it
+jt AND jv -> jw
+jc AND je -> jf
+du OR dt -> dv
+NOT fx -> fy
+aw AND ay -> az
+ge LSHIFT 15 -> gi
+NOT ak -> al
+fm OR fn -> fo
+ff AND fh -> fi
+ci RSHIFT 5 -> cl
+cz OR cy -> da
+NOT ey -> ez
+NOT ju -> jv
+NOT ls -> lt
+kk AND kv -> kx
+NOT ii -> ij
+kl AND kr -> kt
+jk LSHIFT 15 -> jo
+e OR f -> g
+NOT bs -> bt
+hi AND hk -> hl
+hz OR ik -> il
+ek AND em -> en
+ao OR an -> ap
+dv LSHIFT 1 -> ep
+an LSHIFT 15 -> ar
+fo RSHIFT 1 -> gh
+NOT im -> in
+kk RSHIFT 1 -> ld
+hw LSHIFT 1 -> iq
+ec AND ee -> ef
+hb LSHIFT 1 -> hv
+kb AND kd -> ke
+x AND ai -> ak
+dd AND do -> dq
+aq OR ar -> as
+iq OR ip -> ir
+dl AND dn -> do
+iu RSHIFT 5 -> ix
+as OR bd -> be
+NOT go -> gp
+fk OR fj -> fl
+jm LSHIFT 1 -> kg
+NOT cv -> cw
+dp AND dr -> ds
+dt LSHIFT 15 -> dx
+et RSHIFT 1 -> fm
+dy RSHIFT 3 -> ea
+fp AND fv -> fx
+NOT p -> q
+dd RSHIFT 2 -> de
+eu AND fa -> fc
+ba AND bc -> bd
+dh AND dj -> dk
+lr AND lt -> lu
+he RSHIFT 1 -> hx
+ex AND ez -> fa
+df OR dg -> dh
+fj LSHIFT 15 -> fn
+NOT kx -> ky
+gk OR gq -> gr
+dy RSHIFT 2 -> dz
+gh OR gi -> gj
+lj AND ll -> lm
+x OR ai -> aj
+bz AND cb -> cc
+1 AND lu -> lv
+as RSHIFT 3 -> au
+ce OR cd -> cf
+il AND in -> io
+dd RSHIFT 1 -> dw
+NOT lo -> lp
+c LSHIFT 1 -> t
+dd RSHIFT 3 -> df
+dd RSHIFT 5 -> dg
+lh AND li -> lk
+lf RSHIFT 5 -> li
+dy RSHIFT 5 -> eb
+NOT kt -> ku
+at OR az -> ba
+x RSHIFT 3 -> z
+NOT lk -> ll
+lb OR la -> lc
+1 AND r -> s
+lh OR li -> lj
+ln AND lp -> lq
+kk RSHIFT 5 -> kn
+ea OR eb -> ec
+ci AND ct -> cv
+b RSHIFT 2 -> d
+jp RSHIFT 1 -> ki
+NOT cr -> cs
+NOT jd -> je
+jp RSHIFT 2 -> jq
+jn OR jo -> jp
+lf RSHIFT 3 -> lh
+1 AND ds -> dt
+lf AND lq -> ls
+la LSHIFT 15 -> le
+NOT fg -> fh
+at AND az -> bb
+au AND av -> ax
+kw AND ky -> kz
+v OR w -> x
+kk OR kv -> kw
+ks AND ku -> kv
+kh LSHIFT 1 -> lb
+1 AND kz -> la
+NOT kc -> kd
+x RSHIFT 2 -> y
+et OR fe -> ff
+et AND fe -> fg
+NOT ac -> ad
+jl OR jk -> jm
+1 AND jj -> jk
+bn RSHIFT 1 -> cg
+NOT kp -> kq
+ci RSHIFT 3 -> ck
+ev AND ew -> ey
+1 AND ke -> kf
+cj AND cp -> cr
+ir LSHIFT 1 -> jl
+NOT gw -> gx
+as RSHIFT 2 -> at
+iu RSHIFT 1 -> jn
+cy LSHIFT 15 -> dc
+hg OR hh -> hi
+ci RSHIFT 1 -> db
+au OR av -> aw
+km AND kn -> kp
+gj RSHIFT 1 -> hc
+iu RSHIFT 2 -> iv
+ab AND ad -> ae
+da LSHIFT 1 -> du
+NOT bw -> bx
+km OR kn -> ko
+ko AND kq -> kr
+bv AND bx -> by
+kl OR kr -> ks
+1 AND ht -> hu
+df AND dg -> di
+NOT ag -> ah
+d OR j -> k
+d AND j -> l
+b AND n -> p
+gf OR ge -> gg
+gg LSHIFT 1 -> ha
+bn RSHIFT 5 -> bq
+bo OR bu -> bv
+1 AND gy -> gz
+s LSHIFT 15 -> w
+NOT ie -> if
+as RSHIFT 5 -> av
+bo AND bu -> bw
+hz AND ik -> im
+bp AND bq -> bs
+b RSHIFT 1 -> v
+NOT l -> m
+bp OR bq -> br
+g AND i -> j
+br AND bt -> bu
+t OR s -> u
+hz RSHIFT 5 -> ic
+gk AND gq -> gs
+fl LSHIFT 1 -> gf
+he RSHIFT 3 -> hg
+gz LSHIFT 15 -> hd
+hf OR hl -> hm
+1 AND gd -> ge
+fo OR fz -> ga
+id AND if -> ig
+fo AND fz -> gb
+gr AND gt -> gu
+he OR hp -> hq
+fq AND fr -> ft
+ga AND gc -> gd
+fo RSHIFT 2 -> fp
+gl OR gm -> gn
+hg AND hh -> hj
+NOT hn -> ho
+gl AND gm -> go
+he RSHIFT 5 -> hh
+NOT gb -> gc
+hq AND hs -> ht
+hz RSHIFT 3 -> ib
+hz RSHIFT 2 -> ia
+fq OR fr -> fs
+hx OR hy -> hz
+he AND hp -> hr
+gj RSHIFT 5 -> gm
+hf AND hl -> hn
+hv OR hu -> hw
+NOT hj -> hk
+gj RSHIFT 3 -> gl
+fo RSHIFT 3 -> fq
+he RSHIFT 2 -> hf