+extern tree fold_unary (enum tree_code, tree, tree);
+extern tree fold_binary (enum tree_code, tree, tree, tree);
+extern tree fold_ternary (enum tree_code, tree, tree, tree, tree);
+extern tree fold_build1 (enum tree_code, tree, tree);
+extern tree fold_build2 (enum tree_code, tree, tree, tree);
+extern tree fold_build3 (enum tree_code, tree, tree, tree, tree);