diff --git a/solutions/elixir/triangle/1/lib/triangle.ex b/solutions/elixir/triangle/1/lib/triangle.ex
new file mode 100644
index 0000000..b795919
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+++ b/solutions/elixir/triangle/1/lib/triangle.ex
@@ -0,0 +1,19 @@
+defmodule Triangle do
+  @type kind :: :equilateral | :isosceles | :scalene
+
+  @doc """
+  Return the kind of triangle of a triangle with 'a', 'b' and 'c' as lengths.
+  """
+  @spec kind(number, number, number) :: {:ok, kind} | {:error, String.t()}
+  def kind(a, b, c) when a <= 0 or b <= 0 or c <= 0, do: {:error, "all side lengths must be positive"}
+  def kind(a, a, a), do: {:ok, :equilateral}
+  def kind(a, b, c) when a + b >= c and b + c >= a and c + a >= b do
+    case {a, b, c} do
+      {side, side, _} -> {:ok, :isosceles}
+      {side, _, side} -> {:ok, :isosceles}
+      {_, side, side} -> {:ok, :isosceles}
+      _ -> {:ok, :scalene}
+    end
+  end
+  def kind(_, _, _), do: {:error, "side lengths violate triangle inequality"}
+end