diff --git a/src/runtime/c/pgf/aligner.c b/src/runtime/c/pgf/aligner.c
index be7034f58..d143850d6 100644
--- a/src/runtime/c/pgf/aligner.c
+++ b/src/runtime/c/pgf/aligner.c
@@ -176,13 +176,20 @@ pgf_aligner_lzn_symbol_capit(PgfLinFuncs** funcs, PgfCapitState capit)
 	alin->capit = capit;
 }
 
+static void
+pgf_aligner_lzn_symbol_meta(PgfLinFuncs** funcs, PgfMetaId id)
+{
+	pgf_aligner_lzn_symbol_token(funcs, "?");
+}
+
 static PgfLinFuncs pgf_file_lin_funcs = {
 	.symbol_token = pgf_aligner_lzn_symbol_token,
 	.begin_phrase = pgf_aligner_lzn_begin_phrase,
 	.end_phrase   = pgf_aligner_lzn_end_phrase,
 	.symbol_ne    = pgf_aligner_lzn_symbol_ne,
 	.symbol_bind  = pgf_aligner_lzn_symbol_bind,
-	.symbol_capit = pgf_aligner_lzn_symbol_capit
+	.symbol_capit = pgf_aligner_lzn_symbol_capit,
+	.symbol_meta  = pgf_aligner_lzn_symbol_meta
 };
 
 GuSeq*
diff --git a/src/runtime/c/pgf/graphviz.c b/src/runtime/c/pgf/graphviz.c
index 0a7b6d30a..0936a2d63 100644
--- a/src/runtime/c/pgf/graphviz.c
+++ b/src/runtime/c/pgf/graphviz.c
@@ -174,13 +174,26 @@ pgf_bracket_lzn_end_phrase(PgfLinFuncs** funcs, PgfCId cat, int fid, int lindex,
 	state->parent = state->parent->parent;
 }
 
+static void
+pgf_bracket_lzn_symbol_meta(PgfLinFuncs** funcs, PgfMetaId meta_id)
+{
+	PgfBracketLznState* state = gu_container(funcs, PgfBracketLznState, funcs);
+
+	PgfParseNode* node = gu_new(PgfParseNode, state->pool);
+	node->id     = 100000 + gu_buf_length(state->leaves);
+	node->parent = state->parent;
+	node->label  = "?";
+	gu_buf_push(state->leaves, PgfParseNode*, node);
+}
+
 static PgfLinFuncs pgf_bracket_lin_funcs = {
 	.symbol_token  = pgf_bracket_lzn_symbol_token,
 	.begin_phrase  = pgf_bracket_lzn_begin_phrase,
 	.end_phrase    = pgf_bracket_lzn_end_phrase,
 	.symbol_ne     = NULL,
 	.symbol_bind   = NULL,
-	.symbol_capit  = NULL
+	.symbol_capit  = NULL,
+	.symbol_meta   = pgf_bracket_lzn_symbol_meta
 };
 
 static void
diff --git a/src/runtime/c/pgf/linearizer.c b/src/runtime/c/pgf/linearizer.c
index 68a2e1415..a921de61a 100644
--- a/src/runtime/c/pgf/linearizer.c
+++ b/src/runtime/c/pgf/linearizer.c
@@ -111,7 +111,10 @@ pgf_print_cnc_tree(PgfCncTree ctree, GuOut* out, GuExn* err)
 		PgfCncTreeChunks* chunks = ti.data;
 		if (chunks->n_vars+chunks->n_args > 0) gu_putc('(', out, err);
 		pgf_print_cnc_tree_vars(chunks->n_vars, chunks->context, out, err);
-		gu_putc('?', out, err);
+		if (chunks->id > 0)
+			gu_printf(out, err, "?%d", chunks->id);
+		else
+			gu_putc('?', out, err);
 		for (size_t i = 0; i < chunks->n_args; i++) {
 			gu_putc(' ', out, err);
 			pgf_print_cnc_tree(chunks->args[i], out, err);
@@ -361,6 +364,7 @@ pgf_cnc_resolve(PgfCnc* cnc,
 			goto done;
 		}
 		case PGF_EXPR_META: {
+			PgfExprMeta* emeta = i.data;
 			size_t n_args = gu_buf_length(args);
 
 			PgfCncTree chunks_tree;
@@ -368,9 +372,10 @@ pgf_cnc_resolve(PgfCnc* cnc,
 				gu_new_flex_variant(PGF_CNC_TREE_CHUNKS,
 				                    PgfCncTreeChunks,
 				                    args, n_args, &chunks_tree, pool);
+			chunks->id      = emeta->id;
 			chunks->n_vars  = n_vars;
 			chunks->context = context;
-			chunks->n_args = n_args;
+			chunks->n_args  = n_args;
 
 			for (size_t i = 0; i < n_args; i++) {
 				PgfExpr earg = gu_buf_get(args, PgfExpr, n_args-i-1);
@@ -773,13 +778,25 @@ pgf_lzr_cache_symbol_capit(PgfLinFuncs** funcs, PgfCapitState capit)
 	event->tag     = (capit == PGF_CAPIT_ALL) ? PGF_CACHED_ALL_CAPIT : PGF_CACHED_CAPIT;
 }
 
+static void
+pgf_lzr_cache_symbol_meta(PgfLinFuncs** funcs, PgfMetaId id)
+{
+	PgfLzrCache* cache = gu_container(funcs, PgfLzrCache, funcs);
+
+	pgf_lzr_cache_flush(cache, cache->kp->default_form);
+	if ((*cache->lzr->funcs)->symbol_meta) {
+		(*cache->lzr->funcs)->symbol_meta(cache->lzr->funcs, id);
+	}
+}
+
 static PgfLinFuncs pgf_lzr_cache_funcs = {
 	.symbol_token = pgf_lzr_cache_symbol_token,
 	.begin_phrase = pgf_lzr_cache_begin_phrase,
 	.end_phrase   = pgf_lzr_cache_end_phrase,
 	.symbol_ne    = pgf_lzr_cache_symbol_ne,
 	.symbol_bind  = pgf_lzr_cache_symbol_bind,
-	.symbol_capit = pgf_lzr_cache_symbol_capit
+	.symbol_capit = pgf_lzr_cache_symbol_capit,
+	.symbol_meta  = pgf_lzr_cache_symbol_meta
 };
 
 static void
@@ -943,8 +960,8 @@ pgf_lzr_linearize_tree(PgfLzr* lzr, PgfCncTree ctree, size_t lin_idx)
 		PgfCncTreeChunks* fchunks = cti.data;
 
 		if (fchunks->n_args == 0) {
-			if ((*lzr->funcs)->symbol_token) {
-				(*lzr->funcs)->symbol_token(lzr->funcs, "?");
+			if ((*lzr->funcs)->symbol_meta) {
+				(*lzr->funcs)->symbol_meta(lzr->funcs, fchunks->id);
 			}
 		} else {
 			for (size_t i = 0; i < fchunks->n_args; i++) {
@@ -1055,7 +1072,7 @@ pgf_file_lzn_symbol_token(PgfLinFuncs** funcs, PgfToken tok)
 		gu_string_write(tok, flin->out, flin->err);
 		flin->capit = PGF_CAPIT_NONE;
 		break;
-	}	
+	}
 	case PGF_CAPIT_ALL:
 		flin->capit = PGF_CAPIT_NEXT;
 		// continue
@@ -1092,13 +1109,33 @@ pgf_file_lzn_symbol_capit(PgfLinFuncs** funcs, PgfCapitState capit)
 	flin->capit = capit;
 }
 
+static void
+pgf_file_lzn_symbol_meta(PgfLinFuncs** funcs, PgfMetaId id)
+{
+	PgfSimpleLin* flin = gu_container(funcs, PgfSimpleLin, funcs);
+	if (!gu_ok(flin->err)) {
+		return;
+	}
+
+	if (flin->bind)
+		flin->bind = false;
+	else {
+		gu_putc(' ', flin->out, flin->err);
+		if (flin->capit == PGF_CAPIT_NEXT)
+			flin->capit = PGF_CAPIT_NONE;
+	}
+
+	gu_putc('?', flin->out, flin->err);		
+}
+
 static PgfLinFuncs pgf_file_lin_funcs = {
 	.symbol_token = pgf_file_lzn_symbol_token,
 	.begin_phrase = NULL,
 	.end_phrase   = NULL,
 	.symbol_ne    = pgf_file_lzn_symbol_ne,
 	.symbol_bind  = pgf_file_lzn_symbol_bind,
-	.symbol_capit = pgf_file_lzn_symbol_capit
+	.symbol_capit = pgf_file_lzn_symbol_capit,
+	.symbol_meta  = pgf_file_lzn_symbol_meta
 };
 
 PGF_API void
diff --git a/src/runtime/c/pgf/linearizer.h b/src/runtime/c/pgf/linearizer.h
index 816181090..f2fea4221 100644
--- a/src/runtime/c/pgf/linearizer.h
+++ b/src/runtime/c/pgf/linearizer.h
@@ -33,6 +33,8 @@ typedef struct {
 } PgfCncTreeApp;
 
 typedef struct {
+	PgfMetaId id;
+
 	size_t n_vars;
 	PgfPrintContext* context;
 
@@ -94,6 +96,9 @@ struct PgfLinFuncs
 
 	/// capitalization
 	void (*symbol_capit)(PgfLinFuncs** self, PgfCapitState capit);
+	
+	/// meta variable
+	void (*symbol_meta)(PgfLinFuncs** self, PgfMetaId id);
 };
 
 /// Linearize a concrete syntax tree.
diff --git a/src/runtime/c/pgf/lookup.c b/src/runtime/c/pgf/lookup.c
index 27e126d66..16874eb0e 100644
--- a/src/runtime/c/pgf/lookup.c
+++ b/src/runtime/c/pgf/lookup.c
@@ -634,6 +634,7 @@ pgf_lookup_extract(PgfLookupState* st, PgfCCat* ccat)
 			gu_new_flex_variant(PGF_CNC_TREE_CHUNKS,
 			                    PgfCncTreeChunks,
 			                    args, 0, &capp->args[0], st->pool);
+		chunks->id      = 0;
 		chunks->n_vars  = 0;
 		chunks->context = NULL;
 		chunks->n_args  = 0;
@@ -736,7 +737,8 @@ pgf_lookup_compute_kernel_helper(GuBuf* sentence_tokens, GuBuf* expr_tokens,
 				PgfInputToken* sentence_token = gu_buf_index(sentence_tokens, PgfInputToken, l);
 				PgfInputToken* expr_token     = gu_buf_index(expr_tokens, PgfInputToken, k-1);
 
-				if (strcmp(sentence_token->token, expr_token->token) == 0) {
+				if (sentence_token->token != NULL && expr_token->token != NULL &&
+				    strcmp(sentence_token->token, expr_token->token) == 0) {
 					score += 1 + pgf_lookup_compute_kernel_helper(sentence_tokens, expr_tokens, matrix, l, k-1);
 				} else {
 					bool match = false;
@@ -803,10 +805,10 @@ pgf_lookup_ctree_to_expr(PgfCncTree ctree, PgfExprProb* ep,
 		PgfCncTreeChunks* fchunks = cti.data;
 		n_args = fchunks->n_args;
 		args   = fchunks->args;
-		
+
 		ep->expr = gu_new_variant_i(out_pool, 
 		                            PGF_EXPR_META, PgfExprMeta,
-		                            .id = 0);
+		                            .id = fchunks->id);
 		ep->prob = 0;
 		break;
 	}
@@ -887,13 +889,23 @@ pgf_lookup_end_phrase(PgfLinFuncs** self, PgfCId cat, int fid, int lindex, PgfCI
 	st->curr_absfun = NULL;
 }
 
+static void
+pgf_lookup_symbol_meta(PgfLinFuncs** self, PgfMetaId meta_id)
+{
+	PgfLookupState* st = gu_container(self, PgfLookupState, funcs);
+	PgfInputToken* tok = gu_buf_extend(st->expr_tokens);
+	tok->token  = NULL;
+	tok->n_funs = 0;
+}
+
 static PgfLinFuncs pgf_lookup_lin_funcs = {
 	.symbol_token = pgf_lookup_symbol_token,
 	.begin_phrase = pgf_lookup_begin_phrase,
 	.end_phrase   = pgf_lookup_end_phrase,
 	.symbol_ne    = NULL,
 	.symbol_bind  = NULL,
-	.symbol_capit = NULL
+	.symbol_capit = NULL,
+	.symbol_meta  = pgf_lookup_symbol_meta
 };
 
 PGF_API GuEnum*
diff --git a/src/runtime/c/pgf/parseval.c b/src/runtime/c/pgf/parseval.c
index 5f8a3b363..85df380fa 100644
--- a/src/runtime/c/pgf/parseval.c
+++ b/src/runtime/c/pgf/parseval.c
@@ -59,7 +59,7 @@ pgf_metrics_lzn_end_phrase1(PgfLinFuncs** funcs, PgfCId cat, int fid, int lin_id
 
 	int start = gu_buf_pop(state->marks, int);
 	int end   = state->pos;
-	
+
 	if (start != end) {
 		PgfPhrase* phrase = gu_new(PgfPhrase, state->pool);
 		phrase->start = start;
@@ -110,13 +110,26 @@ pgf_metrics_lzn_end_phrase2(PgfLinFuncs** funcs, PgfCId cat, int fid, int lin_id
 	}
 }
 
+static void
+pgf_metrics_lzn_symbol_meta(PgfLinFuncs** funcs, PgfMetaId meta_id)
+{
+	PgfMetricsLznState* state = gu_container(funcs, PgfMetricsLznState, funcs);
+
+	pgf_metrics_put_space(state);
+	if (state->out != NULL)
+		gu_putc('?', state->out, state->err);
+
+	state->pos += 1;
+}
+
 static PgfLinFuncs pgf_metrics_lin_funcs1 = {
 	.symbol_token = pgf_metrics_lzn_symbol_token,
 	.begin_phrase = pgf_metrics_lzn_begin_phrase,
 	.end_phrase   = pgf_metrics_lzn_end_phrase1,
 	.symbol_ne    = pgf_metrics_symbol_ne,
 	.symbol_bind  = pgf_metrics_symbol_bind,
-	.symbol_capit = NULL
+	.symbol_capit = NULL,
+	.symbol_meta  = pgf_metrics_lzn_symbol_meta
 };
 
 static PgfLinFuncs pgf_metrics_lin_funcs2 = {
@@ -125,7 +138,8 @@ static PgfLinFuncs pgf_metrics_lin_funcs2 = {
 	.end_phrase   = pgf_metrics_lzn_end_phrase2,
 	.symbol_ne    = pgf_metrics_symbol_ne,
 	.symbol_bind  = pgf_metrics_symbol_bind,
-	.symbol_capit = NULL
+	.symbol_capit = NULL,
+	.symbol_meta  = pgf_metrics_lzn_symbol_meta
 };
 
 PGF_API bool
diff --git a/src/runtime/dotNet/Bracket.cs b/src/runtime/dotNet/Bracket.cs
index 8fa005704..1fc4c0db7 100644
--- a/src/runtime/dotNet/Bracket.cs
+++ b/src/runtime/dotNet/Bracket.cs
@@ -52,7 +52,8 @@ namespace PGFSharp
 					end_phrase = EndPhrase,
 					symbol_ne = null,
 					symbol_bind = null,
-					symbol_capit = null
+					symbol_capit = null,
+					symbol_meta = SymbolMeta
 				};
 			}
 
@@ -80,6 +81,10 @@ namespace PGFSharp
 				else 
 					stack.Peek ().AddChild (b);
 			}
+			
+			private void SymbolMeta(IntPtr self, int meta_id) {
+				stack.Peek().AddChild(new StringChildBracket("?"));
+			}
 
 			public Bracket Build() {
 				return final;
diff --git a/src/runtime/dotNet/Native.cs b/src/runtime/dotNet/Native.cs
index 346f85905..5c750e010 100644
--- a/src/runtime/dotNet/Native.cs
+++ b/src/runtime/dotNet/Native.cs
@@ -221,6 +221,9 @@ namespace PGFSharp
         [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
         public delegate void LinFuncSymbolCapitalization(IntPtr self);
 
+        [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
+        public delegate void LinFuncSymbolMeta(IntPtr self, int meta_id);
+
         [StructLayout(LayoutKind.Sequential)]
         public struct PgfLinFuncs
         {
@@ -241,6 +244,9 @@ namespace PGFSharp
 
             [MarshalAs(UnmanagedType.FunctionPtr)]
             public LinFuncSymbolCapitalization symbol_capit;
+            
+            [MarshalAs(UnmanagedType.FunctionPtr)]
+            public LinFuncSymbolMeta symbol_meta;
         }
 
         #endregion
diff --git a/src/runtime/java/jpgf.c b/src/runtime/java/jpgf.c
index c7957b317..6e3d07d72 100644
--- a/src/runtime/java/jpgf.c
+++ b/src/runtime/java/jpgf.c
@@ -951,13 +951,20 @@ pgf_bracket_lzn_end_phrase(PgfLinFuncs** funcs, PgfCId cat, int fid, int lindex,
 	state->list = parent;
 }
 
+static void
+pgf_bracket_lzn_symbol_meta(PgfLinFuncs** funcs, PgfMetaId id)
+{
+	pgf_bracket_lzn_symbol_token(funcs, "?");
+}
+
 static PgfLinFuncs pgf_bracket_lin_funcs = {
 	.symbol_token  = pgf_bracket_lzn_symbol_token,
 	.begin_phrase  = pgf_bracket_lzn_begin_phrase,
 	.end_phrase    = pgf_bracket_lzn_end_phrase,
 	.symbol_ne     = NULL,
 	.symbol_bind   = NULL,
-	.symbol_capit  = NULL
+	.symbol_capit  = NULL,
+	.symbol_meta   = pgf_bracket_lzn_symbol_meta
 };
 
 JNIEXPORT jobjectArray JNICALL 
diff --git a/src/runtime/python/pypgf.c b/src/runtime/python/pypgf.c
index d8a3ac976..0278d4bd1 100644
--- a/src/runtime/python/pypgf.c
+++ b/src/runtime/python/pypgf.c
@@ -2039,13 +2039,20 @@ pgf_bracket_lzn_end_phrase(PgfLinFuncs** funcs, PgfCId cat, int fid, int lindex,
 	state->list = parent;
 }
 
+static void
+pgf_bracket_lzn_symbol_meta(PgfLinFuncs** funcs, PgfMetaId meta_id)
+{
+	pgf_bracket_lzn_symbol_token(funcs, "?");
+}
+
 static PgfLinFuncs pgf_bracket_lin_funcs = {
 	.symbol_token  = pgf_bracket_lzn_symbol_token,
 	.begin_phrase  = pgf_bracket_lzn_begin_phrase,
 	.end_phrase    = pgf_bracket_lzn_end_phrase,
 	.symbol_ne     = NULL,
 	.symbol_bind   = NULL,
-	.symbol_capit  = NULL
+	.symbol_capit  = NULL,
+	.symbol_meta   = pgf_bracket_lzn_symbol_meta
 };
 
 static PyObject*