diff --git a/haskell/03-functions/functions.hs b/haskell/03-functions/functions.hs
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+
+-- single parameter
+
+-- two parameters
+
+-- ============= pattern matching =================
+
+-- ============= guards =================
+
+-- ============= recursive algorithms =================
+
+-- ============= recursive list algorithms =================
+
+-- ============= merge sort =================
+
+-- =========== Filter all numbers that can be divided by 10 ===========
+
+-- ========================== standard deviation using lambdas =====================
+-- The standard deviation is a measure of the amount of variation or dispersion of a set of values.
+-- It is defined as the square root of the average of the squared differences from the mean.
+--
+-- Formula:
+--   σ = sqrt( (1/N) * Σ (xi - μ)^2 )
+-- where:
+--   - σ is the standard deviation,
+--   - N is the number of values,
+--   - xi represents each value,
+--   - μ is the mean of the values.
+
+stddev seq = 0
+
+-- ======================= order list of strings by length =================
+