diff --git a/pl/arith.yap b/pl/arith.yap
index 131cbdfcc..3c3989e17 100644
--- a/pl/arith.yap
+++ b/pl/arith.yap
@@ -399,40 +399,40 @@ succ(M,N) :-
 	N < 0,
 	'$do_error'(domain_error(not_less_than_zero, N),succ(M,N)).
 
-plus(X, Y, Z) :
+plus(X, Y, Z) :-
        (
         var(X)
-       >
+       ->
         (
          integer(Y), integer(Z)
-        >
+        ->
          '$minus'(Z,Y,X)
         ;
          '$plus_error'(X,Y,Z)
         )
        ;
         integer(X)
-       >
+       ->
         (
          var(Y)
-        >
+        ->
          (
           integer(Z)
-         >
+         ->
           '$minus'(Z,X,Y)
          ;
          '$plus_error'(X,Y,Z)
          )
         ;
          integer(Y)
-        >
+        ->
          (
           integer(Z)
-         >
+         ->
           '$minus'(Z,Y,X)
          ;
           var(Z)
-         >
+         ->
           '$plus'(X,Y,Z)
          ;
           '$plus_error'(X,Y,Z)