diff --git a/PyTeX/build/build/pytex_file.py b/PyTeX/build/build/pytex_file.py
index e84b15d..c875a39 100644
--- a/PyTeX/build/build/pytex_file.py
+++ b/PyTeX/build/build/pytex_file.py
@@ -40,7 +40,7 @@ class PyTeXSourceFile:
         self._file_hash = md5(self._relative_path.path)
 
     @property
-    def relative_path(self):
+    def relative_path(self) -> RelativePath:
         return self._relative_path
 
     @property
diff --git a/PyTeX/build/build/pytex_output_file.py b/PyTeX/build/build/pytex_output_file.py
new file mode 100644
index 0000000..c25c58a
--- /dev/null
+++ b/PyTeX/build/build/pytex_output_file.py
@@ -0,0 +1,34 @@
+from pathlib import Path
+from typing import Optional, Union, List, Tuple
+
+from .enums import PyTeXRootDirType
+from .pytex_config import PyTeXConfig
+from ...logger import logger
+from .constants import *
+from ..versioning.version_info.version_info import VersionInfo, FileVersionInfo
+from .pytex_file import PyTeXSourceFile
+from .relative_path import RelativePath
+from .hashing import md5
+
+
+class PyTeXOutputFile:
+    def __init__(
+            self,
+            source_file: PyTeXSourceFile,
+            output_file: RelativePath,
+            last_version_info: FileVersionInfo
+    ):
+        self.output_file: RelativePath = output_file
+        self.source_file: PyTeXSourceFile = source_file
+        self.last_version_info: FileVersionInfo = last_version_info
+
+    @property
+    def dependencies(self) -> List[str]:
+        return self.source_file.formatter.dependencies
+
+    def is_recent(self) -> bool:
+        return self.last_version_info.file_hash == self.source_file.file_hash
+
+    @property
+    def file_hash(self) -> str:
+        return md5(self.output_file.path)
diff --git a/PyTeX/format/dict_formatter.py b/PyTeX/format/dict_formatter.py
index eb40017..2ccbc56 100644
--- a/PyTeX/format/dict_formatter.py
+++ b/PyTeX/format/dict_formatter.py
@@ -22,6 +22,7 @@ class DictFormatter(PyTeXFormatter):
         self._dict_name = self.input_file.name.split('.')[0]
         self._translations = None
 
+    @property
     def dependencies(self) -> List[str]:
         return []  # No dependencies for dictionaries
 
diff --git a/PyTeX/format/pytex_formatter.py b/PyTeX/format/pytex_formatter.py
index cc361d6..cb5ef09 100644
--- a/PyTeX/format/pytex_formatter.py
+++ b/PyTeX/format/pytex_formatter.py
@@ -102,9 +102,9 @@ class PyTeXFormatter(FormatterIF, ABC):
                     or self.config.include_repo_version
                     or self.config.include_repo_info_text
             ):
-                self._header = GenericText([])
+                self._header = GenericText()
             else:
-                self._header = GenericText([])
+                self._header = GenericText()
                 # TODO: handle license
                 if self.config.include_extra_header:
                     self._header += self.config.extra_header + ['']
diff --git a/PyTeX/format/simple_tex_formatter.py b/PyTeX/format/simple_tex_formatter.py
index 7a7d05f..f911065 100644
--- a/PyTeX/format/simple_tex_formatter.py
+++ b/PyTeX/format/simple_tex_formatter.py
@@ -10,7 +10,7 @@ class SimpleTeXFormatter(TexFormatter):
         if out_file.exists():
             raise NotImplementedError
         else:
-            self._output_file = out_file.open()
+            self._output_file = out_file.open('w')
 
     def close_output_stream(self):
         self._output_file.close()
@@ -18,6 +18,7 @@ class SimpleTeXFormatter(TexFormatter):
     def future_config(self) -> List[Tuple[str, FormattingConfig]]:
         return []  # TODO
 
+    @property
     def dependencies(self) -> List[str]:
         return []  # sty / cls file does not depend on anything