Add combintatorics HW1

Change-Id: Iaab537215d740a3f5f8bdaf48e365690c699c906
diff --git a/quad9/combinatorics/combinatorics_defs.tex b/quad9/combinatorics/combinatorics_defs.tex
new file mode 100644
index 0000000..0cb107c
--- /dev/null
+++ b/quad9/combinatorics/combinatorics_defs.tex
@@ -0,0 +1 @@
+\newcommand*{\Seq}[0]{\text{Seq}}