diff --git a/aoc.bqn b/aoc.bqn
index 9ee3e24..4df2e71 100644
--- a/aoc.bqn
+++ b/aoc.bqn
@@ -7,8 +7,9 @@ Split ⇐ {(⊏ ∾ 1⊸↓¨∘(1⊸↓)) Sub⟜𝕩¨ (» ⋈¨ ⊢-») /𝕨=
 Day1 ⇐ (⊑ ⋈ (+´3⊸↑))∘(∨+´¨)∘Split∘(•BQN⎊0¨)∘•FLines
 
 Day2 ⇐ {
-  Line ← -⟜"AX"∘∾ ' '⊸Split
   B ← ⊣ (A ← {1+𝕩+3×3|1+𝕩-𝕨}) {3|𝕨+𝕩-1}
-  +´˘⍉ (A≍B)´∘Line˘ >•FLines 𝕩
+  +´˘⍉ (A≍B)´∘{a‿s‿b:⟨a-'A',b-'X'⟩}˘ >•FLines 𝕩
 }
-# •Show Day2 ⊑•args
+•Show Day2 ⊑•args
+
+# day 3 maybe later
diff --git a/aoc.m b/aoc.m
index f108fa1..ef32f1d 100644
--- a/aoc.m
+++ b/aoc.m
@@ -33,6 +33,8 @@ main2(!IO) :-
 solution(1, day1.run).
 :- import_module day2.
 solution(2, day2.run).
+:- import_module day3.
+solution(3, day3.run).
 
 :- pred run_day(int, part, list(string), univ).
 :- mode run_day(in, in, in, out) is cc_multi.
diff --git a/basics.m b/basics.m
index 236595e..b28338b 100644
--- a/basics.m
+++ b/basics.m
@@ -23,6 +23,16 @@
 :- mode wrap_main(pred(di, uo) is det,      di, uo) is cc_multi.
 
 
+:- import_module char.
+
+:- type chars == list(char).
+
+
+:- import_module int.
+
+:- func sum(list(int)) = int.
+
+
 :- import_module maybe.
 
 :- func to_int_may(string) = maybe(int).
@@ -57,5 +67,8 @@ read_lines_need(File, Lines, !IO) :-
   need(Res, Lines).
 
 
+sum(Xs) = foldl(plus, Xs, 0).
+
+
 to_int_may(Str) = Out :-
   if to_int(Str, N) then Out = yes(N) else Out = no.
diff --git a/day1.m b/day1.m
index df3589d..3676d28 100644
--- a/day1.m
+++ b/day1.m
@@ -27,6 +27,3 @@ gather(Xs) = Ys :- gather(Xs, Ys).
 gather([],            [[]]).
 gather([no     | Xs], [[]       | Yss]) :- gather(Xs, Yss).
 gather([yes(Y) | Xs], [[Y | Ys] | Yss]) :- gather(Xs, [Ys | Yss]).
-
-:- func sum(list(int)) = int.
-sum(Xs) = foldl(plus, Xs, 0).
diff --git a/day2.m b/day2.m
index d291e4d..3a6dac3 100644
--- a/day2.m
+++ b/day2.m
@@ -22,8 +22,6 @@
 :- type result ---> me; you; draw.
 :- type move_res == pair(move, result).
 
-:- type chars == list(char).
-
 :- type parser(T) == (pred(T, chars, chars)).
 :- mode parser(I) == (pred(out(I), in, out) is semidet).
 :- mode parser    == parser(ground).
@@ -89,9 +87,6 @@ score1(You, Me) = to_int(Me) + win_score(Res) :- win(You, Me, Res).
 :- func score2(move, result) = int.
 score2(You, Res) = to_int(Me) + win_score(Res) :- win(You, Me, Res).
 
-:- func sum(list(int)) = int.
-sum(Xs) = foldl(plus, Xs, 0).
-
 
 :- pred run(list(string)::in, parser(pair(T, U))::parser,
             (func(T, U) = int)::in, int::out) is det.
diff --git a/day3.m b/day3.m
new file mode 100644
index 0000000..d9a6745
--- /dev/null
+++ b/day3.m
@@ -0,0 +1,59 @@
+:- module day3.
+:- interface.
+:- import_module basics.
+:- import_module list.
+:- import_module univ.
+
+:- pred run(part::in, list(string)::in, univ::out) is cc_multi.
+
+:- implementation.
+:- import_module int.
+:- import_module char.
+:- import_module string.
+:- import_module exception.
+
+:- pred split(chars::in, chars::out, chars::out) is semidet.
+split(X, L, H) :-
+  Len = length(X), even(Len),
+  split_list(Len / 2, X, L, H).
+
+:- pred common(list(chars)::in, char::out) is nondet.
+common([S | Ss], C) :- member(C, S), (Ss = [] ; common(Ss, C)).
+
+:- func score(char) = int.
+score(C) = I :-
+  if is_lower(C) then
+    I = to_int(C) - to_int('a') + 1
+  else
+    I = to_int(C) - to_int('A') + 27.
+
+:- pred threes(list(T)::in, list(list(T))::out) is semidet.
+threes([],               []).
+threes([X, Y, Z | Rest], [[X, Y, Z] | Groups]) :- threes(Rest, Groups).
+
+
+:- pred go1(string::in, int::out) is cc_multi.
+go1(Line, Out) :-
+  if split(to_char_list(Line), Fst, Snd),
+     common([Fst, Snd], C)
+  then
+    Out = score(C)
+  else
+    die("invalid line: ""%s""", [s(Line)]).
+
+
+:- pred go2(list(string)::in, int::out) is cc_multi.
+go2(Lines, Score) :-
+  if common(map(to_char_list, Lines), C) then
+    Score = score(C)
+  else
+    die("no item in common").
+
+
+run(one, Lines, univ(sum(Scores))) :-
+  map(go1, Lines, Scores).
+run(two, Lines, univ(sum(Scores))) :-
+  if threes(Lines, Groups) then
+    map(go2, Groups, Scores)
+  else
+    die("not a multiple of three lines").