Add two- and three-argument commands for union and intersection.

diff --git a/mjo-common.tex b/mjo-common.tex
index efa10a26045d9f199bd3bdb1f8c9f5ec97c1cb19..b269417749dcf12738b968645a0083c7aa033ed2 100644 (file)
--- a/mjo-common.tex
+++ b/mjo-common.tex
@@ -71,3 +71,20 @@
 \providecommand*{\Cn}[1][n]{
   \mathbb{C}\if\detokenize{#1}\detokenize{1}{}\else^{#1}\fi
 }
+
+
+%
+% Basic set operations
+%
+
+% The union of its two arguments.
+\providecommand*{\union}[2]{ {#1} \cup {#2} }
+
+% A three-argument union.
+\providecommand*{\unionthree}[3]{ \union{\union{#1}{#2}}{#3} }
+
+% The intersection of its two arguments.
+\providecommand*{\intersect}[2]{ {#1} \cap {#2} }
+
+% A three-argument intersection.
+\providecommand*{\intersectthree}[3]{ \intersect{\intersect{#1}{#2}}{#3} }