diff --git a/src/8-misc/random.cpp b/src/8-misc/random.cpp
index 43e856a..12700bd 100644
--- a/src/8-misc/random.cpp
+++ b/src/8-misc/random.cpp
@@ -1,28 +1,8 @@
 #include "../common/common.hpp"
 
-// what: tiny RNG wrapper with fixed default seed for reproducible tests/shuffles.
-// time: O(1) per call; memory: O(1)
-// constraint: uses mt19937_64.
-// usage: rng rd(2); ll x = rd.ll_range(l, r); rd.shuf(v);
-struct rng {
-    static constexpr ull DEFAULT_SEED = 712367;
-    mt19937_64 eng;
-
-    rng(ull seed = DEFAULT_SEED) : eng(seed) {}
-
-    ll ll_range(ll l, ll r) {
-        // edge: l <= r
-        uniform_int_distribution<ll> dis(l, r);
-        return dis(eng);
-    }
-
-    int int_range(int l, int r) {
-        uniform_int_distribution<int> dis(l, r);
-        return dis(eng);
-    }
-
-    template <class T>
-    void shuf(vector<T> &v) {
-        shuffle(all(v), eng);
-    }
-};
+// what: mt19937_64 quick usage snippet (time-seeded + rand range + shuffle).
+// time: O(1) per draw; memory: O(1)
+// constraint: uniform_int_distribution is inclusive [l, r].
+// constraint: chrono seed isn't cryptographically secure.
+// usage: mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
+// usage: ll x = uniform_int_distribution<ll>(l, r)(rng); shuffle(all(v), rng);
diff --git a/tests/8-misc/test_random.cpp b/tests/8-misc/test_random.cpp
deleted file mode 100644
index 258ada4..0000000
--- a/tests/8-misc/test_random.cpp
+++ /dev/null
@@ -1,30 +0,0 @@
-#include "../../src/8-misc/random.cpp"
-
-// what: tests for rng helper (reproducibility).
-// time: O(n); memory: O(n)
-// constraint: fixed seed.
-// usage: g++ -std=c++17 test_random.cpp && ./a.out
-
-void test_repro() {
-    rng a(2), b(2);
-    for (int i = 0; i < 100; i++) {
-        assert(a.int_range(-5, 5) == b.int_range(-5, 5));
-        assert(a.ll_range(-100, 100) == b.ll_range(-100, 100));
-    }
-}
-
-void test_shuffle() {
-    vector<int> v(50), w(50);
-    iota(v.begin(), v.end(), 0);
-    w = v;
-    rng a(7), b(7);
-    a.shuf(v);
-    b.shuf(w);
-    assert(v == w);
-}
-
-int main() {
-    test_repro();
-    test_shuffle();
-    return 0;
-}