diff --git a/Envelope_2/doc_tex/Envelope_2/main.tex b/Envelope_2/doc_tex/Envelope_2/main.tex
index 934e33cbf3d..f7084920204 100644
--- a/Envelope_2/doc_tex/Envelope_2/main.tex
+++ b/Envelope_2/doc_tex/Envelope_2/main.tex
@@ -25,6 +25,7 @@
 \newcommand{\calC}{{\cal C}}
 \newcommand{\calL}{{\cal L}}
 \newcommand{\calU}{{\cal U}}
+\newcommand{\calP}{{\cal P}}
 \newcommand{\eps}{{\varepsilon}}
 \newcommand{\Cpp}{{C}{\tt ++}}