diff --git a/library/matrix.yap b/library/matrix.yap
index bfeb266d0..806a9e5e5 100644
--- a/library/matrix.yap
+++ b/library/matrix.yap
@@ -775,6 +775,9 @@ rhs(log(RHS), Logs ) :- !,
 rhs(exp(RHS), Logs ) :- !,
 	rhs(RHS, X1),
 	matrix_to_exps( X1, Logs ).
+rhs(sum(RHS), Logs ) :- !,
+	rhs(RHS, X1),
+	matrix_sum( X1, Logs ).
 rhs(S, NS) :-
 	rhs_opaque( S ), !,
 	S = NS.
diff --git a/library/system.yap b/library/system.yap
index 3cbdcfa34..2749489b1 100644
--- a/library/system.yap
+++ b/library/system.yap
@@ -788,15 +788,17 @@ path.
 The predicates performs a left-recursive traversal. It does not protect against file system errors and it does not check for symbolic links.
 
 */
-directory_map(D, P),
+directory_map(D, P) :-
         working_directory(_, D),
 	list_directory(D,L),
 	d_map(L, P).
 
 d_map([],_,_,_).
 d_map(['.'|Fs],D, P) :-
+    !,
     d_map(Fs,D, P).
 d_map(['..'|Fs],D, P) :-
+    !,
     d_map(Fs, D, P).
 d_map([D|Fs], D, P) :-
     absolute_file_name( F, File, [prefix(D)] ),