Splice ./universe directory into ./

Manually merging:
- README.md: I added the description from universe/README.md into the heading of
  dotfiles/README.md.
- .envrc: dotfiles/.envrc was a superset of universe/.envrc
- .gitignore: Adding some of the ignored patterns from universe/.gitignore to
  dotfiles/.gitignore

Everything else here should be a simple rename.

11 files changed, 773 insertions, 0 deletions

diff --git a/advent-of-code/aoc2019.nix b/advent-of-code/aoc2019.nix
new file mode 100644
index 000000000000..10e6c559a9b4
--- /dev/null
+++ b/advent-of-code/aoc2019.nix
@@ -0,0 +1,8 @@
+with import <nixpkgs> {};
+with python35Packages;
+
+buildPythonPackage {
+  name = "wpcarro";
+  src = ./day_5.py;
+  propagatedBuildInputs = [ pytest numpy ];
+}
diff --git a/advent-of-code/day_1.py b/advent-of-code/day_1.py
new file mode 100644
index 000000000000..bd4024e3ec7d
--- /dev/null
+++ b/advent-of-code/day_1.py
@@ -0,0 +1,119 @@
+from math import floor
+
+xs = [
+    102473,
+    84495,
+    98490,
+    68860,
+    62204,
+    72810,
+    65185,
+    145951,
+    77892,
+    108861,
+    70764,
+    67286,
+    74002,
+    80773,
+    52442,
+    131505,
+    107162,
+    126993,
+    59784,
+    64231,
+    91564,
+    68585,
+    98735,
+    69020,
+    77332,
+    60445,
+    65826,
+    111506,
+    95431,
+    146687,
+    135119,
+    86804,
+    95915,
+    85434,
+    111303,
+    148127,
+    132921,
+    136213,
+    89004,
+    143137,
+    144853,
+    143017,
+    104386,
+    100612,
+    54760,
+    63813,
+    144191,
+    84481,
+    69718,
+    84936,
+    98621,
+    124993,
+    92736,
+    60369,
+    137284,
+    101902,
+    112726,
+    51784,
+    126496,
+    85005,
+    101661,
+    137278,
+    136637,
+    90340,
+    100209,
+    53683,
+    50222,
+    132060,
+    98797,
+    139054,
+    135638,
+    100632,
+    137849,
+    125333,
+    103981,
+    76954,
+    134352,
+    74229,
+    93402,
+    62552,
+    50286,
+    57066,
+    98439,
+    120708,
+    117827,
+    107884,
+    72837,
+    148663,
+    125645,
+    61460,
+    120555,
+    142473,
+    106668,
+    58612,
+    58576,
+    143366,
+    90058,
+    121087,
+    89546,
+    126161,
+]
+
+
+def fuel_for_mass(x):
+    """Return the amount of fuel (in mass) required for a mass of X. The total
+    amount of fuel includes the amount of fuel required for the fuel itself,
+    since fuel also has a mass weights."""
+    mass_fuel = floor(x / 3) - 2
+    if mass_fuel < 0:
+        return 0
+    else:
+        fuel_fuel = fuel_for_mass(mass_fuel)
+        return mass_fuel + fuel_fuel
+
+
+print(sum(fuel_for_mass(x) for x in xs))
diff --git a/advent-of-code/day_2.py b/advent-of-code/day_2.py
new file mode 100644
index 000000000000..77774c1bb5ad
--- /dev/null
+++ b/advent-of-code/day_2.py
@@ -0,0 +1,32 @@
+from itertools import product
+
+x = [
+    1, 0, 0, 3, 1, 1, 2, 3, 1, 3, 4, 3, 1, 5, 0, 3, 2, 1, 10, 19, 1, 6, 19, 23,
+    2, 23, 6, 27, 2, 6, 27, 31, 2, 13, 31, 35, 1, 10, 35, 39, 2, 39, 13, 43, 1,
+    43, 13, 47, 1, 6, 47, 51, 1, 10, 51, 55, 2, 55, 6, 59, 1, 5, 59, 63, 2, 9,
+    63, 67, 1, 6, 67, 71, 2, 9, 71, 75, 1, 6, 75, 79, 2, 79, 13, 83, 1, 83, 10,
+    87, 1, 13, 87, 91, 1, 91, 10, 95, 2, 9, 95, 99, 1, 5, 99, 103, 2, 10, 103,
+    107, 1, 107, 2, 111, 1, 111, 5, 0, 99, 2, 14, 0, 0
+]
+
+
+def interpret(i, x):
+    op, a, b, out = x[i + 0], x[i + 1], x[i + 2], x[i + 3]
+    if op == 1:
+        x[out] = x[a] + x[b]
+        return interpret(i + 4, x)
+    elif op == 2:
+        x[out] = x[a] * x[b]
+        return interpret(i + 4, x)
+    elif op == 99:
+        return x
+    else:
+        raise Exception('Unsupported opcode: {}. {}, {}'.format(op, a, b))
+
+
+for a, b in product(range(100), range(100)):
+    y = x[:]
+    y[1] = a
+    y[2] = b
+    if interpret(0, y)[0] == 19690720:
+        print(100 * a + b)
diff --git a/advent-of-code/day_3.py b/advent-of-code/day_3.py
new file mode 100644
index 000000000000..6dd863528c1c
--- /dev/null
+++ b/advent-of-code/day_3.py
@@ -0,0 +1,137 @@
+from math import floor
+from heapq import heappush, heappop
+
+xs = [
+    "R1009", "U993", "L383", "D725", "R163", "D312", "R339", "U650", "R558",
+    "U384", "R329", "D61", "L172", "D555", "R160", "D972", "L550", "D801",
+    "L965", "U818", "L123", "D530", "R176", "D353", "L25", "U694", "L339",
+    "U600", "L681", "D37", "R149", "D742", "R762", "U869", "R826", "U300",
+    "L949", "U978", "L303", "U361", "R136", "D343", "L909", "U551", "R745",
+    "U913", "L566", "D292", "R820", "U886", "R205", "D431", "L93", "D71",
+    "R577", "U872", "L705", "U510", "L698", "U963", "R607", "U527", "L669",
+    "D543", "R690", "U954", "L929", "D218", "R490", "U500", "L589", "D332",
+    "R949", "D538", "R696", "U659", "L188", "U468", "L939", "U833", "L445",
+    "D430", "R78", "D303", "R130", "D649", "R849", "D712", "L511", "U745",
+    "R51", "U973", "R799", "U829", "R605", "D771", "L837", "U204", "L414",
+    "D427", "R538", "U116", "R540", "D168", "R493", "U900", "L679", "U431",
+    "L521", "D500", "L428", "U332", "L954", "U717", "L853", "D339", "L88",
+    "U807", "L607", "D496", "L163", "U468", "L25", "U267", "L759", "D898",
+    "L591", "U445", "L469", "U531", "R596", "D486", "L728", "D677", "R350",
+    "D429", "R39", "U568", "R92", "D875", "L835", "D841", "R877", "U178",
+    "L221", "U88", "R592", "U692", "R455", "U693", "L419", "U90", "R609",
+    "U672", "L293", "U168", "R175", "D456", "R319", "D570", "R504", "D165",
+    "L232", "D624", "L604", "D68", "R807", "D59", "R320", "D281", "L371",
+    "U956", "L788", "D897", "L231", "D829", "R287", "D798", "L443", "U194",
+    "R513", "D925", "L232", "U225", "L919", "U563", "R448", "D889", "R661",
+    "U852", "L950", "D558", "L269", "U186", "L625", "U673", "L995", "U732",
+    "R435", "U849", "L413", "D690", "L158", "D234", "R361", "D458", "L271",
+    "U90", "L781", "U754", "R256", "U162", "L842", "U927", "L144", "D62",
+    "R928", "D238", "R473", "U97", "L745", "U303", "L487", "D349", "L520",
+    "D31", "L825", "U385", "L133", "D948", "L39", "U62", "R801", "D664",
+    "L333", "U134", "R692", "U385", "L658", "U202", "L279", "D374", "R489",
+    "D686", "L182", "U222", "R733", "U177", "R94", "D603", "L376", "U901",
+    "R216", "D851", "L155", "D214", "L460", "U758", "R121", "D746", "L180",
+    "U175", "L943", "U146", "L166", "D251", "L238", "U168", "L642", "D341",
+    "R281", "U182", "R539", "D416", "R553", "D67", "L748", "U272", "R257",
+    "D869", "L340", "U180", "R791", "U138", "L755", "D976", "R731", "U713",
+    "R602", "D284", "L258", "U176", "R509", "U46", "R935", "U576", "R96",
+    "U89", "L913", "U703", "R833"
+]
+ys = [
+    "L1006", "D998", "R94", "D841", "R911", "D381", "R532", "U836", "L299",
+    "U237", "R781", "D597", "L399", "D800", "L775", "D405", "L485", "U636",
+    "R589", "D942", "L878", "D779", "L751", "U711", "L973", "U410", "L151",
+    "U15", "L685", "U417", "L106", "D648", "L105", "D461", "R448", "D743",
+    "L589", "D430", "R883", "U37", "R155", "U350", "L421", "U23", "R337",
+    "U816", "R384", "D671", "R615", "D410", "L910", "U914", "L579", "U385",
+    "R916", "U13", "R268", "D519", "R289", "U410", "L389", "D885", "L894",
+    "U734", "L474", "U707", "L72", "U155", "L237", "U760", "L127", "U806",
+    "L15", "U381", "L557", "D727", "L569", "U320", "L985", "D452", "L8",
+    "D884", "R356", "U732", "L672", "D458", "L485", "U402", "L238", "D30",
+    "R644", "U125", "R753", "U183", "L773", "U487", "R849", "U210", "L164",
+    "D808", "L595", "D668", "L340", "U785", "R313", "D72", "L76", "D263",
+    "R689", "U604", "R471", "U688", "R462", "D915", "R106", "D335", "R869",
+    "U499", "R190", "D916", "R468", "D882", "R56", "D858", "L143", "D741",
+    "L386", "U856", "R50", "U853", "R151", "D114", "L773", "U854", "L290",
+    "D344", "L23", "U796", "L531", "D932", "R314", "U960", "R643", "D303",
+    "L661", "D493", "L82", "D491", "L722", "U848", "L686", "U4", "L985",
+    "D509", "L135", "D452", "R500", "U105", "L326", "D101", "R222", "D944",
+    "L645", "D362", "L628", "U305", "L965", "U356", "L358", "D137", "R787",
+    "U728", "R967", "U404", "R18", "D928", "L695", "D965", "R281", "D597",
+    "L791", "U731", "R746", "U163", "L780", "U41", "L255", "U81", "L530",
+    "D964", "R921", "D297", "R475", "U663", "L226", "U623", "L984", "U943",
+    "L143", "U201", "R926", "U572", "R343", "U839", "R764", "U751", "R128",
+    "U939", "R987", "D108", "R474", "U599", "R412", "D248", "R125", "U797",
+    "L91", "D761", "L840", "U290", "L281", "U779", "R650", "D797", "R185",
+    "D320", "L25", "U378", "L696", "U332", "R75", "D620", "L213", "D667",
+    "R558", "U267", "L846", "U306", "R939", "D220", "R311", "U827", "R345",
+    "U534", "R56", "D679", "R48", "D845", "R898", "U8", "R862", "D960", "R753",
+    "U319", "L886", "D795", "R805", "D265", "R876", "U729", "R894", "D368",
+    "R858", "U744", "R506", "D327", "L903", "U919", "L721", "U507", "L463",
+    "U753", "R775", "D719", "R315", "U128", "R17", "D376", "R999", "D386",
+    "L259", "U181", "L162", "U605", "L265", "D430", "R35", "D968", "R207",
+    "U466", "R796", "D667", "R93", "U749", "L315", "D410", "R312", "U929",
+    "L923", "U260", "R638"
+]
+
+
+def to_coords(xs):
+    row, col = 0, 0
+    coords = []
+    for x in xs:
+        d, amt = x[0], int(x[1:])
+        if d == 'U':
+            for i in range(1, amt + 1):
+                coords.append((row + i, col))
+            row += amt
+        elif d == 'D':
+            for i in range(1, amt + 1):
+                coords.append((row - i, col))
+            row -= amt
+        elif d == 'L':
+            for i in range(1, amt + 1):
+                coords.append((row, col - i))
+            col -= amt
+        elif d == 'R':
+            for i in range(1, amt + 1):
+                coords.append((row, col + i))
+            col += i
+    return coords
+
+
+def contains(row, col, d):
+    if row not in d:
+        return False
+    return col in d[row]
+
+
+def intersections(xs, ys):
+    d = {}
+    ints = set()
+    for row, col in to_coords(xs):
+        if row in d:
+            d[row].add(col)
+        else:
+            d[row] = {col}
+    for row, col in to_coords(ys):
+        if contains(row, col, d):
+            ints.add((row, col))
+    return ints
+
+
+def trace_to(coord, xs):
+    count = 0
+    for coord_x in to_coords(xs):
+        count += 1
+        if coord_x == coord:
+            return count
+    raise Exception("Intersection doesn't exist")
+
+
+answer = []
+for coord in intersections(xs, ys):
+    x = trace_to(coord, xs)
+    y = trace_to(coord, ys)
+    heappush(answer, x + y)
+
+print(heappop(answer))
diff --git a/advent-of-code/day_4.py b/advent-of-code/day_4.py
new file mode 100644
index 000000000000..adef73b452dc
--- /dev/null
+++ b/advent-of-code/day_4.py
@@ -0,0 +1,35 @@
+import re
+
+start = 134792
+end = 675810
+
+
+def satisfies(x):
+    x = str(x)
+    result = False
+    double, not_decreasing = False, False
+
+    # double and *only* double exists
+    for i in range(len(x) - 1):
+        # double and left-of-a  is BOL or !x
+        #        and right-of-b is EOL or !x
+        a, b = x[i], x[i + 1]
+        bol = i - 1 < 0
+        eol = i + 2 >= len(x)
+        if a == b and (bol or x[i - 1] != a) and (eol or x[i + 2] != a):
+            double = True
+            break
+
+    # not_decreasing
+    prev = int(x[0])
+    for a in x[1:]:
+        a = int(a)
+        if prev > a:
+            return False
+        prev = a
+    not_decreasing = True
+
+    return double and not_decreasing
+
+
+print(len([x for x in range(start, end + 1) if satisfies(x)]))
diff --git a/advent-of-code/day_5.ex b/advent-of-code/day_5.ex
new file mode 100644
index 000000000000..807e3c9177be
--- /dev/null
+++ b/advent-of-code/day_5.ex
@@ -0,0 +1,50 @@
+defmodule Interpretter do
+  def interpret_param({mode, x}, xs) do
+    case mode do
+      :positional -> Enum.at(xs, x)
+      :immediate  -> x
+    end
+  end
+
+  # Perhaps I can model the intepretter after Forth and make it a stack-based
+  # interpretter with an emphasis on debugability, introspection.
+  def interpret(i, xs) do
+    stack = []
+    op = Enum.at(xs, i)
+
+    # map instructions into an intermediate representation (i.e. IR) where the
+    # opcodes are mapped into atoms and the arguments are mapped into references
+    # or literals.
+
+    instructions =
+      %{'01' => :add,
+        '02' => :multiply,
+        '03' => :input,
+        '04' => :output,
+        '05' => :jump_if_true,
+        '06' => :jump_if_false,
+        '07' => :less_than,
+        '08' => :equal_to,
+        '99' => :return}
+
+    case xs do
+      [:add, a, b, {:positional, out} | rest] ->
+        a = interpret_param(a, xs)
+        b = interpret_param(b, xs)
+        Interpretter.interpret(i + 3, List.insert_at(xs, out, a + b))
+
+      [:multiply, a, b, {:positional, out} | rest] ->
+        a = interpret_param(a, xs)
+        b = interpret_param(b, xs)
+        Interpretter.interpret(i + 3, List.insert_at(xs, out, a * b))
+
+      [:input, a | rest] -> nil
+      [:output, a | rest] -> nil
+      [:jump_if_true, a, b | rest] -> nil
+      [:jump_if_false, a, b | rest] -> nil
+      [:less_than, a, b, out | rest] -> nil
+      [:equal_to, a, b, out | rest] -> nil
+      [:return | _rest] -> nil
+    end
+  end
+end
diff --git a/advent-of-code/day_5.py b/advent-of-code/day_5.py
new file mode 100644
index 000000000000..3d82846e6126
--- /dev/null
+++ b/advent-of-code/day_5.py
@@ -0,0 +1,170 @@
+x = [
+    3, 225, 1, 225, 6, 6, 1100, 1, 238, 225, 104, 0, 1102, 31, 68, 225, 1001,
+    13, 87, 224, 1001, 224, -118, 224, 4, 224, 102, 8, 223, 223, 1001, 224, 7,
+    224, 1, 223, 224, 223, 1, 174, 110, 224, 1001, 224, -46, 224, 4, 224, 102,
+    8, 223, 223, 101, 2, 224, 224, 1, 223, 224, 223, 1101, 13, 60, 224, 101,
+    -73, 224, 224, 4, 224, 102, 8, 223, 223, 101, 6, 224, 224, 1, 224, 223,
+    223, 1101, 87, 72, 225, 101, 47, 84, 224, 101, -119, 224, 224, 4, 224,
+    1002, 223, 8, 223, 1001, 224, 6, 224, 1, 223, 224, 223, 1101, 76, 31, 225,
+    1102, 60, 43, 225, 1102, 45, 31, 225, 1102, 63, 9, 225, 2, 170, 122, 224,
+    1001, 224, -486, 224, 4, 224, 102, 8, 223, 223, 101, 2, 224, 224, 1, 223,
+    224, 223, 1102, 29, 17, 224, 101, -493, 224, 224, 4, 224, 102, 8, 223, 223,
+    101, 1, 224, 224, 1, 223, 224, 223, 1102, 52, 54, 225, 1102, 27, 15, 225,
+    102, 26, 113, 224, 1001, 224, -1560, 224, 4, 224, 102, 8, 223, 223, 101, 7,
+    224, 224, 1, 223, 224, 223, 1002, 117, 81, 224, 101, -3645, 224, 224, 4,
+    224, 1002, 223, 8, 223, 101, 6, 224, 224, 1, 223, 224, 223, 4, 223, 99, 0,
+    0, 0, 677, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1105, 0, 99999, 1105, 227, 247,
+    1105, 1, 99999, 1005, 227, 99999, 1005, 0, 256, 1105, 1, 99999, 1106, 227,
+    99999, 1106, 0, 265, 1105, 1, 99999, 1006, 0, 99999, 1006, 227, 274, 1105,
+    1, 99999, 1105, 1, 280, 1105, 1, 99999, 1, 225, 225, 225, 1101, 294, 0, 0,
+    105, 1, 0, 1105, 1, 99999, 1106, 0, 300, 1105, 1, 99999, 1, 225, 225, 225,
+    1101, 314, 0, 0, 106, 0, 0, 1105, 1, 99999, 8, 226, 677, 224, 102, 2, 223,
+    223, 1005, 224, 329, 1001, 223, 1, 223, 1108, 677, 226, 224, 102, 2, 223,
+    223, 1006, 224, 344, 101, 1, 223, 223, 108, 677, 226, 224, 102, 2, 223,
+    223, 1006, 224, 359, 101, 1, 223, 223, 7, 677, 226, 224, 102, 2, 223, 223,
+    1005, 224, 374, 101, 1, 223, 223, 1007, 226, 677, 224, 102, 2, 223, 223,
+    1005, 224, 389, 101, 1, 223, 223, 8, 677, 677, 224, 102, 2, 223, 223, 1006,
+    224, 404, 1001, 223, 1, 223, 1007, 677, 677, 224, 1002, 223, 2, 223, 1006,
+    224, 419, 101, 1, 223, 223, 1108, 677, 677, 224, 1002, 223, 2, 223, 1005,
+    224, 434, 1001, 223, 1, 223, 1107, 226, 677, 224, 102, 2, 223, 223, 1005,
+    224, 449, 101, 1, 223, 223, 107, 226, 226, 224, 102, 2, 223, 223, 1006,
+    224, 464, 101, 1, 223, 223, 1108, 226, 677, 224, 1002, 223, 2, 223, 1005,
+    224, 479, 1001, 223, 1, 223, 7, 677, 677, 224, 102, 2, 223, 223, 1006, 224,
+    494, 1001, 223, 1, 223, 1107, 677, 226, 224, 102, 2, 223, 223, 1005, 224,
+    509, 101, 1, 223, 223, 107, 677, 677, 224, 1002, 223, 2, 223, 1006, 224,
+    524, 101, 1, 223, 223, 1008, 677, 677, 224, 1002, 223, 2, 223, 1006, 224,
+    539, 101, 1, 223, 223, 7, 226, 677, 224, 1002, 223, 2, 223, 1005, 224, 554,
+    101, 1, 223, 223, 108, 226, 226, 224, 1002, 223, 2, 223, 1006, 224, 569,
+    101, 1, 223, 223, 1008, 226, 677, 224, 102, 2, 223, 223, 1005, 224, 584,
+    101, 1, 223, 223, 8, 677, 226, 224, 1002, 223, 2, 223, 1005, 224, 599, 101,
+    1, 223, 223, 1007, 226, 226, 224, 1002, 223, 2, 223, 1005, 224, 614, 101,
+    1, 223, 223, 1107, 226, 226, 224, 1002, 223, 2, 223, 1006, 224, 629, 101,
+    1, 223, 223, 107, 677, 226, 224, 1002, 223, 2, 223, 1005, 224, 644, 1001,
+    223, 1, 223, 1008, 226, 226, 224, 1002, 223, 2, 223, 1006, 224, 659, 101,
+    1, 223, 223, 108, 677, 677, 224, 1002, 223, 2, 223, 1005, 224, 674, 1001,
+    223, 1, 223, 4, 223, 99, 226
+]
+
+# Interpretter spec:
+# Op-code width: 2
+# ABCDE
+# A:  Mode of 3rd parameter
+# B:  Mode of 2rd parameter
+# C:  Mode of 1st parameter
+# DE: 2-digit op-code
+#
+# Not every op-code has the same arity.
+#
+# Parameter modes:
+# - positional: index of memory. 0
+# - immediate: raw value. 1
+# Assert that you never attempt to write to an "immediate value"
+
+# Parameter modes
+POS = '0'  # positional parameter mode
+VAL = '1'  # immediate parameter mode
+
+
+# Pasted from day-2.py
+# interpretter :: Int -> [Int] -> [Int] -> IO ()
+def interpret(i, x, argv=[], outs=[]):
+    """Values in `argv` will be applied to any `input` fields."""
+    # The widest op-code we'll see is 3 + 2 = 5 for either addition or
+    # multiplication since each of those is a 3-arity function with a two-digit
+    # op-code.
+    instruction = '{:05d}'.format(x[i])
+    op = instruction[-2:]
+
+    if op == '01':
+        a, b, out = x[i + 1], x[i + 2], x[i + 3]
+        mode_a, mode_b, mode_out = instruction[2], instruction[1], instruction[
+            0]
+        a = a if mode_a == VAL else x[a]
+        b = b if mode_b == VAL else x[b]
+        assert mode_out == POS
+        x[out] = a + b
+        return interpret(i + 4, x, argv=argv, outs=outs)
+    elif op == '02':
+        a, b, out = x[i + 1], x[i + 2], x[i + 3]
+        mode_a, mode_b, mode_out = instruction[2], instruction[1], instruction[
+            0]
+        a = a if mode_a == VAL else x[a]
+        b = b if mode_b == VAL else x[b]
+        assert mode_out == POS
+        x[out] = a * b
+        return interpret(i + 4, x, argv=argv, outs=outs)
+    # input
+    elif op == '03':
+        a = x[i + 1]
+        mode_a = instruction[2]
+        assert mode_a == POS
+        # What's the pythonic way to defensively get this value?
+        if len(argv) and argv[0] is not None:
+            x[a] = argv[0]
+            return interpret(i + 2, x, argv=argv[1:], outs=outs)
+        elif len(outs) and outs[-1] is not None:
+            x[a] = outs[-1]
+            return interpret(i + 2, x, argv=argv, outs=outs)
+        else:
+            # Here we want to block until the user applies input. This could be
+            # done easily with message passing for something similar.
+            x[a] = int(input('Enter: '))
+            return interpret(i + 2, x, argv=argv)
+    # output
+    elif op == '04':
+        a = x[i + 1]
+        mode_a = instruction[2]
+        a = a if mode_a == VAL else x[a]
+        outs.append(a)
+        return interpret(i + 2, x, argv=argv, outs=outs)
+    # jump-if-true
+    elif op == '05':
+        a, b = x[i + 1], x[i + 2]
+        mode_a, mode_b = instruction[2], instruction[1]
+        a = a if mode_a == VAL else x[a]
+        b = b if mode_b == VAL else x[b]
+        if a != 0:
+            return interpret(b, x, argv=argv, outs=outs)
+        else:
+            return interpret(i + 3, x, argv=argv, outs=outs)
+    # jump-if-false
+    elif op == '06':
+        a, b = x[i + 1], x[i + 2]
+        mode_a, mode_b = instruction[2], instruction[1]
+        a = a if mode_a == VAL else x[a]
+        b = b if mode_b == VAL else x[b]
+        if a == 0:
+            return interpret(b, x, argv=argv, outs=outs)
+        else:
+            return interpret(i + 3, x, argv=argv, outs=outs)
+        pass
+    # less than
+    elif op == '07':
+        a, b, out = x[i + 1], x[i + 2], x[i + 3]
+        mode_a, mode_b, mode_out = instruction[2], instruction[1], instruction[
+            0]
+        a = a if mode_a == VAL else x[a]
+        b = b if mode_b == VAL else x[b]
+        assert mode_out == POS
+        if a < b:
+            x[out] = 1
+        else:
+            x[out] = 0
+        return interpret(i + 4, x, argv=argv, outs=outs)
+    # equals
+    elif op == '08':
+        a, b, out = x[i + 1], x[i + 2], x[i + 3]
+        mode_a, mode_b, mode_out = instruction[2], instruction[1], instruction[
+            0]
+        a = a if mode_a == VAL else x[a]
+        b = b if mode_b == VAL else x[b]
+        assert mode_out == POS
+        if a == b:
+            x[out] = 1
+        else:
+            x[out] = 0
+        return interpret(i + 4, x, argv=argv, outs=outs)
+    elif op == '99':
+        return x[0]
+    else:
+        raise Exception('Unsupported opcode: {}.'.format(op))
diff --git a/advent-of-code/day_5.pyc b/advent-of-code/day_5.pyc
new file mode 100644
index 000000000000..d95573e94326
--- /dev/null
+++ b/advent-of-code/day_5.pyc
Binary files differdiff --git a/advent-of-code/day_6.py b/advent-of-code/day_6.py
new file mode 100644
index 000000000000..aba99b8239ff
--- /dev/null
+++ b/advent-of-code/day_6.py
@@ -0,0 +1,155 @@
+from graphviz import Digraph
+
+data = """6WF)DRK 2PT)PSM H42)FN8 1XR)LQD HRK)9KL TD6)H8W 98Z)BJM RCQ)LVG
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+1DQ)CYC WNP)DM8 CBJ)LK7 ZT8)FWY LQD)PNN 555)9Z3 TNS)D9L QMF)L11 FR8)5RH WF9)R87
+NKG)5HT L5G)91W N2Z)YV9 9B5)CD7 ZV7)8NQ ST6)74T ZJ6)CQV S18)47M 74T)8YN WNH)TN2
+874)46H 3VV)PZ3 Y1F)42W MPT)2LP FDR)HWF X7G)RTK 52B)P4R RYP)G93 NWH)YCF 7TR)FB8
+RWQ)6FH 8F8)HLC CRN)P2P B6D)KC5 PNN)HRG""".split()
+
+# COM is the root in this tree
+
+
+# parent :: Vertex -> [Edge] -> Maybe(Vertex)
+def parent(x, xs):
+    for a, b in xs:
+        if b == x:
+            return a
+    return None
+
+
+# parents :: Vertex -> [Edge] -> [Vertex]
+def parents(x, xs):
+    parents = []
+    p = parent(x, xs)
+    while p:
+        parents.append(p)
+        p = parent(p, xs)
+    return parents
+
+
+# alias Vertex :: String
+# alias Edge :: (String, String)
+# to_edge_list :: [String] -> [(String, String)]
+def to_edge_list(xs):
+    """Returns a list of tuples where (A, B) represents a directed edge from
+    vertex A to vertex B."""
+    return [(x[0:3], x[4:]) for x in xs]
+
+
+# to_graphviz :: [Edge] -> String
+def to_graphviz(xs):
+    d = Digraph()
+    for a, b in xs:
+        d.node(a, label=a)
+        d.edge(a, b)
+    return d.source
+
+
+graph = to_edge_list(data)
+you = parents('YOU', graph)
+san = parents('SAN', graph)
+
+# Distance from YOU to shared point with SAN
+yd = 1
+for i in range(len(you)):
+    if you[i] in san:
+        break
+    yd += 1
+
+# Distance from SAN to shared point with YOU
+sd = 1
+for i in range(len(san)):
+    if san[i] in you:
+        break
+    sd += 1
+
+print('Number of orbital transfers required: {}'.format(yd - 1 + sd - 1))
diff --git a/advent-of-code/day_7.py b/advent-of-code/day_7.py
new file mode 100644
index 000000000000..14597d5104e3
--- /dev/null
+++ b/advent-of-code/day_7.py
@@ -0,0 +1,49 @@
+from day_5 import interpret
+from itertools import permutations
+
+# TODO: I may need to re-write this in Elixir modelling each amplifier as a
+# `Process` and `Process.send`ing each amplifier the signals.
+
+data = [
+    3, 8, 1001, 8, 10, 8, 105, 1, 0, 0, 21, 38, 59, 76, 89, 106, 187, 268, 349,
+    430, 99999, 3, 9, 1002, 9, 3, 9, 101, 2, 9, 9, 1002, 9, 4, 9, 4, 9, 99, 3,
+    9, 1001, 9, 5, 9, 1002, 9, 5, 9, 1001, 9, 2, 9, 1002, 9, 3, 9, 4, 9, 99, 3,
+    9, 1001, 9, 4, 9, 102, 4, 9, 9, 1001, 9, 3, 9, 4, 9, 99, 3, 9, 101, 4, 9,
+    9, 1002, 9, 5, 9, 4, 9, 99, 3, 9, 1002, 9, 3, 9, 101, 5, 9, 9, 1002, 9, 3,
+    9, 4, 9, 99, 3, 9, 102, 2, 9, 9, 4, 9, 3, 9, 1002, 9, 2, 9, 4, 9, 3, 9,
+    1002, 9, 2, 9, 4, 9, 3, 9, 101, 2, 9, 9, 4, 9, 3, 9, 1002, 9, 2, 9, 4, 9,
+    3, 9, 102, 2, 9, 9, 4, 9, 3, 9, 101, 1, 9, 9, 4, 9, 3, 9, 1001, 9, 1, 9, 4,
+    9, 3, 9, 1002, 9, 2, 9, 4, 9, 3, 9, 101, 2, 9, 9, 4, 9, 99, 3, 9, 1002, 9,
+    2, 9, 4, 9, 3, 9, 101, 2, 9, 9, 4, 9, 3, 9, 1002, 9, 2, 9, 4, 9, 3, 9, 101,
+    1, 9, 9, 4, 9, 3, 9, 102, 2, 9, 9, 4, 9, 3, 9, 102, 2, 9, 9, 4, 9, 3, 9,
+    101, 2, 9, 9, 4, 9, 3, 9, 101, 2, 9, 9, 4, 9, 3, 9, 102, 2, 9, 9, 4, 9, 3,
+    9, 1001, 9, 2, 9, 4, 9, 99, 3, 9, 1002, 9, 2, 9, 4, 9, 3, 9, 1001, 9, 2, 9,
+    4, 9, 3, 9, 101, 1, 9, 9, 4, 9, 3, 9, 101, 2, 9, 9, 4, 9, 3, 9, 101, 2, 9,
+    9, 4, 9, 3, 9, 102, 2, 9, 9, 4, 9, 3, 9, 1001, 9, 2, 9, 4, 9, 3, 9, 102, 2,
+    9, 9, 4, 9, 3, 9, 1001, 9, 1, 9, 4, 9, 3, 9, 1001, 9, 2, 9, 4, 9, 99, 3, 9,
+    1001, 9, 2, 9, 4, 9, 3, 9, 102, 2, 9, 9, 4, 9, 3, 9, 1001, 9, 2, 9, 4, 9,
+    3, 9, 102, 2, 9, 9, 4, 9, 3, 9, 101, 2, 9, 9, 4, 9, 3, 9, 1002, 9, 2, 9, 4,
+    9, 3, 9, 1002, 9, 2, 9, 4, 9, 3, 9, 1002, 9, 2, 9, 4, 9, 3, 9, 101, 1, 9,
+    9, 4, 9, 3, 9, 101, 1, 9, 9, 4, 9, 99, 3, 9, 101, 2, 9, 9, 4, 9, 3, 9, 102,
+    2, 9, 9, 4, 9, 3, 9, 1002, 9, 2, 9, 4, 9, 3, 9, 1001, 9, 2, 9, 4, 9, 3, 9,
+    1001, 9, 2, 9, 4, 9, 3, 9, 1001, 9, 2, 9, 4, 9, 3, 9, 1001, 9, 1, 9, 4, 9,
+    3, 9, 1001, 9, 2, 9, 4, 9, 3, 9, 1001, 9, 2, 9, 4, 9, 3, 9, 102, 2, 9, 9,
+    4, 9, 99
+]
+
+data_a, data_b, data_c, data_d, data_e = data[:], data[:], data[:], data[:], data[:]
+
+# m = 0
+# for a, b, c, d, e in permutations(range(5, 10)):
+#     answer = None
+#     z = 0
+#     while z is not None:
+#         print(a, b, c, d, e)
+#         print('---')
+#         v = interpret(0, data_a, argv=[a, z])
+#         print(v)
+#         w = interpret(0, data_b, argv=[b, v])
+#         x = interpret(0, data_c, argv=[c, w])
+#         y = interpret(0, data_d, argv=[d, x])
+#         z = interpret(0, data_e, argv=[e, y])
+#         m = max(m, z)
diff --git a/advent-of-code/writePythonBin.nix b/advent-of-code/writePythonBin.nix
new file mode 100644
index 000000000000..1730edb2ebe4
--- /dev/null
+++ b/advent-of-code/writePythonBin.nix
@@ -0,0 +1,18 @@
+{ pkgs ? import <nixpkgs> {}, ... }:
+
+{ name, deps, src }:
+
+let
+  inherit (pkgs) pythonPackages writeTextFile;
+  inherit (builtins) toFile;
+
+in writeTextFile {
+  inherit name;
+  executable = true;
+  destination = "/bin/${name}";
+
+  text = ''
+    #!/bin/sh
+    ${pkgs.python3}/bin/python3 ${src}
+  '';
+}