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diff --git a/linux/apps/advent2020/1a.mu b/linux/apps/advent2020/1a.mu
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+# https://adventofcode.com/2020/day/1
+#
+# To run (on Linux):
+#   $ git clone https://github.com/akkartik/mu
+#   $ cd mu
+#   $ ./translate apps/advent2020/1a.mu
+#   $ ./a.elf < input
+#   found
+#   1353 667
+#   902451
+#
+# You'll need to register to download the 'input' file for yourself.
+
+fn main -> _/ebx: int {
+  # data structure
+  var numbers-storage: (array int 0x100)  # 256 ints
+  var numbers/esi: (addr array int) <- address numbers-storage
+  var numbers-index/ecx: int <- copy 0
+  # phase 1: parse each line from stdin and add it to numbers
+  {
+    var line-storage: (stream byte 0x100)  # 256 bytes
+    var line/edx: (addr stream byte) <- address line-storage
+    {
+#?       print-string 0, "== iter\n"
+      # read line from stdin
+      clear-stream line
+      read-line-from-real-keyboard line
+      # if line is empty (not even a newline), quit
+      var done?/eax: boolean <- stream-empty? line
+      compare done?, 0/false
+      break-if-!=
+#?       print-stream-to-real-screen line
+      # convert line to int and append it to numbers
+      var n/eax: int <- parse-decimal-int-from-stream line
+#?       print-int32-decimal 0, n
+#?       print-string 0, "\n"
+      var dest/ebx: (addr int) <- index numbers, numbers-index
+      copy-to *dest, n
+      numbers-index <- increment
+#?       print-string 0, "== "
+#?       print-int32-decimal 0, numbers-index
+#?       print-string 0, "\n"
+      loop
+    }
+  }
+  # phase 2: for each number in the array, check if 2020-it is in the rest of
+  # the array
+  var i/eax: int <- copy 0
+  {
+    compare i, numbers-index
+    break-if->=
+    var src/ebx: (addr int) <- index numbers, i
+#?     print-int32-decimal 0, *src
+#?     print-string 0, "\n"
+    var target/ecx: int <- copy 0x7e4  # 2020
+    target <- subtract *src
+    {
+      var found?/eax: boolean <- find-after numbers, i, target
+      compare found?, 0/false
+      break-if-=
+      print-string 0, "found\n"
+      print-int32-decimal 0, *src
+      print-string 0, " "
+      print-int32-decimal 0, target
+      print-string 0, "\n"
+      target <- multiply *src
+      print-int32-decimal 0, target
+      print-string 0, "\n"
+      return 0/success
+    }
+    i <- increment
+    loop
+  }
+  return 1/not-found
+}
+
+fn find-after _numbers: (addr array int), start: int, _target: int -> _/eax: boolean {
+  var numbers/esi: (addr array int) <- copy _numbers
+  var target/edi: int <- copy _target
+  var len/ecx: int <- length numbers
+  var i/eax: int <- copy start
+  i <- increment
+  {
+    compare i, len
+    break-if->=
+    var src/edx: (addr int) <- index numbers, i
+    # if *src == target, return true
+    compare *src, target
+    {
+      break-if-!=
+      return 1/true
+    }
+    i <- increment
+    loop
+  }
+  return 0/false
+}