added missing dependency

diff --git a/helm/software/matita/library/nat/sigma_and_pi.ma b/helm/software/matita/library/nat/sigma_and_pi.ma
index fe3a2d8b5d417502ac99e5572a1a759a7e448bba..84301b49adf80d9aeab35c83b405bf8b50dc71f7 100644 (file)
--- a/helm/software/matita/library/nat/sigma_and_pi.ma
+++ b/helm/software/matita/library/nat/sigma_and_pi.ma
@@ -16,6 +16,7 @@ set "baseuri" "cic:/matita/nat/sigma_and_pi".
 
 include "nat/factorial.ma".
 include "nat/exp.ma".
+include "nat/lt_arith.ma".
 
 let rec sigma n f m \def
   match n with