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diff --git a/challenge-100/abigail/lua/ch-1.lua b/challenge-100/abigail/lua/ch-1.lua
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+++ b/challenge-100/abigail/lua/ch-1.lua
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+#!/opt/local/bin/lua
+
+--
+-- See ../README.md
+--
+
+--
+-- Run as: lua ch-1.lua < input-file
+--
+
+for line in io . lines () do
+    --
+    -- Parse input
+    --
+    local _, _, hour, minute, ampm = line : find ("(%d+):(%d+)%s*([ap]?)m?")
+
+    --
+    -- We need an explicite case to numbers
+    --
+    hour   = tonumber (hour)
+    minute = tonumber (minute)
+
+    --
+    -- Find out what the new AM/PM marker should be:
+    --   - If the current marker is AM or PM, the new one is empty.
+    --   - Else, if the hour is 12 or higher, it's PM
+    --   - Else, it's AM
+    --
+    local new_ampm = ""
+    if   ampm == ""
+    then if   hour >= 12
+         then new_ampm = "pm"
+         else new_ampm = "am"
+         end
+    end
+
+    --
+    -- Calculate the new hours
+    --   - If AM, an hour of 12 becomes 0, and we leave the rest as is
+    --   - If PM, an hour of 12 stays 12, else, we add 12 to the hour
+    --   - If no AM/PM, subtract 12 if the hour is larger than 12;
+    --        add 12 if the hour is 0
+    --
+    hour = hour % 12
+    if   ampm == "" and hour == 0
+    then hour = 12
+    end
+    if   ampm == "p"
+    then hour = hour + 12
+    end
+
+    --
+    -- Print the results
+    --
+    print (string . format ("%02d:%02d%s", hour, minute, new_ampm))
+end