diff --git a/README.md b/README.md
index 59b4b10..fa8d7d1 100644
--- a/README.md
+++ b/README.md
@@ -41,6 +41,8 @@
     * [decompress.cpp](./src/decompress.cpp) (C++) :white_check_mark::microscope:
     * [compress.cpp](./src/compress.cpp) (C++) :white_check_mark::microscope:
     * [decompress.c](./src/decompress.c) (C)
+* [zad. 9.] ile jest trójek spełniających nierówność trójkąta w tablicy
+    * [triangle_inequality](./src/triangle_inequality.c) (C)
 * [zad. 10.] zabawka Jasia
     * [cylinder_toy](./src/cylinder_toy.c) (C)
     * [toy](./src/toy.c): autor: @lbozyk (C) :white_check_mark:
@@ -50,6 +52,8 @@
 * [zad. 12.] następna permutacja
     * [lexicographical_order](./src/lexicographical_order.c) (C)
     * [next_perm](./src/next_perm.c): autor: @lbozyk (C) :white_check_mark:
+* [zad. 13.] sprawdź, czy jeden ciąg zawiera się w drugim
+    * [subsequence](./src/subsequence.c) (C)
 * [zad. 16.] ciąg róznicowy
     * [differential_sequence](./src/differential_sequence.c) (C)
     * [diff_seq](./src/diff_seq.c) (C): autor: @lbozyk (C) :white_check_mark:
diff --git a/src/subsequence.c b/src/subsequence.c
new file mode 100644
index 0000000..1202b5a
--- /dev/null
+++ b/src/subsequence.c
@@ -0,0 +1,70 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+
+void swap(int *a, int *b) {
+    int temp = *a;
+    *a = *b;
+    *b = temp;
+}
+
+int partition(int arr[], int low, int high) {
+    int pivot = arr[high];
+    int i = low;
+
+    for (int j = low; j <= high; j++) {
+        if (arr[j] < pivot) {
+            swap(arr[i], arr[j]);
+            i++;
+        }
+    }
+    swap(arr[i + 1], arr[high]);
+    return (i + 1);
+}
+
+void quick_sort(int arr[], int low, int high) {
+    if (low < high) {
+        int index = partition(arr, low, high);
+
+        quick_sort(arr, low, index - 1);
+        quick_sort(arr, index + 1, high);
+    }
+}
+
+// check if b[] contains all elements of a[]
+bool is_subsequence(int a[], int size_a, int b[], int size_b) {
+    quick_sort(a, 0, size_a);
+    quick_sort(b, 0, size_b);
+
+    int j = 0;
+    for (int i = 0; i < size_a; i++) {
+        if (a[i] < b[i])
+            return false;
+        else if (a[i] > b[i])
+            i--;
+        
+        j++;
+
+        if (j == size_b)
+            return false;
+    }
+
+    return true;
+}
+
+int main() {
+    int size_a, size_b;
+    if(!scanf("%d", &size_a)) printf("invalid value");
+    int* a = (int*)malloc((size_t)size_a * sizeof(int));
+    for (int i = 0; i < size_a; i++) {
+        if(!scanf("%d", &a[i])) printf("invalid value");
+    }
+
+    if(!scanf("%d", &size_b)) printf("invalid value");
+    int* b = (int*)malloc((size_t)size_b * sizeof(int));
+    for (int i = 0; i < size_b; i++) {
+        if(!scanf("%d", &b[i])) printf("invalid value");
+    }
+
+    printf(is_subsequence(a, size_a, b, size_b));
+}
\ No newline at end of file
diff --git a/src/triangle_inequality.c b/src/triangle_inequality.c
new file mode 100644
index 0000000..da272e7
--- /dev/null
+++ b/src/triangle_inequality.c
@@ -0,0 +1,14 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+// tab - all elements sorted in ascending order
+// a < b < c
+// c < a + b
+
+int trojki(int size, int tab[]) { 
+
+}
+
+int main() {
+
+}
\ No newline at end of file
diff --git a/tests/c/subsequence0.in b/tests/c/subsequence0.in
new file mode 100644
index 0000000..8fe67d3
--- /dev/null
+++ b/tests/c/subsequence0.in
@@ -0,0 +1,4 @@
+5
+1 2 3 4 5
+5 
+5 4 3 2 1
\ No newline at end of file
diff --git a/tests/c/subsequence0.out b/tests/c/subsequence0.out
new file mode 100644
index 0000000..56a6051
--- /dev/null
+++ b/tests/c/subsequence0.out
@@ -0,0 +1 @@
+1
\ No newline at end of file
diff --git a/tests/c/subsequence1.in b/tests/c/subsequence1.in
new file mode 100644
index 0000000..7e49b8e
--- /dev/null
+++ b/tests/c/subsequence1.in
@@ -0,0 +1,4 @@
+6
+1 2 3 4 5 6
+5 
+5 4 3 2 1
\ No newline at end of file
diff --git a/tests/c/subsequence1.out b/tests/c/subsequence1.out
new file mode 100644
index 0000000..c227083
--- /dev/null
+++ b/tests/c/subsequence1.out
@@ -0,0 +1 @@
+0
\ No newline at end of file
diff --git a/tests/c/subsequence2.in b/tests/c/subsequence2.in
new file mode 100644
index 0000000..3afa2c1
--- /dev/null
+++ b/tests/c/subsequence2.in
@@ -0,0 +1,4 @@
+6
+1 2 3 4 5 6
+7 
+-1 5 4 3 2 1 100
\ No newline at end of file
diff --git a/tests/c/subsequence2.out b/tests/c/subsequence2.out
new file mode 100644
index 0000000..c227083
--- /dev/null
+++ b/tests/c/subsequence2.out
@@ -0,0 +1 @@
+0
\ No newline at end of file