diff --git a/news/4386.bugfix.rst b/news/4386.bugfix.rst
new file mode 100644
index 00000000..ff633fb9
--- /dev/null
+++ b/news/4386.bugfix.rst
@@ -0,0 +1 @@
+Fix a bug that non-wheel file requirements can be resolved successfully.
diff --git a/news/4441.feature.rst b/news/4441.feature.rst
new file mode 100644
index 00000000..3836516c
--- /dev/null
+++ b/news/4441.feature.rst
@@ -0,0 +1 @@
+Add the missing ``--system`` option to ``pipenv sync``.
diff --git a/news/4443.feature.rst b/news/4443.feature.rst
new file mode 100644
index 00000000..ea4a0c06
--- /dev/null
+++ b/news/4443.feature.rst
@@ -0,0 +1,2 @@
+Add a new option pair ``--header/--no-header`` to ``pipenv lock`` command,
+which adds a header to the generated requirements.txt
diff --git a/pipenv/cli/options.py b/pipenv/cli/options.py
index b96a03f6..35af39ca 100644
--- a/pipenv/cli/options.py
+++ b/pipenv/cli/options.py
@@ -440,6 +440,7 @@ def lock_options(f):
     f = install_base_options(f)
     f = lock_dev_option(f)
     f = emit_requirements_flag(f)
+    f = emit_requirements_header_flag(f)
     f = dev_only_flag(f)
     return f
 
diff --git a/pipenv/core.py b/pipenv/core.py
index 9ba7cf7a..b072d649 100644
--- a/pipenv/core.py
+++ b/pipenv/core.py
@@ -841,15 +841,15 @@ def do_install_dependencies(
     dev = dev or dev_only
     deps_list = list(lockfile.get_requirements(dev=dev, only=dev_only))
     if emit_requirements:
-        index_args = prepare_pip_source_args(get_source_list(pypi_mirror=pypi_mirror, project=project))
+        index_args = prepare_pip_source_args(
+            get_source_list(pypi_mirror=pypi_mirror, project=project)
+        )
         index_args = " ".join(index_args).replace(" -", "\n-")
         deps = [
             req.as_line(sources=False, include_hashes=False) for req in deps_list
         ]
         click.echo(index_args)
-        click.echo(
-            "\n".join(sorted(deps))
-        )
+        click.echo("\n".join(sorted(deps)))
         sys.exit(0)
     if concurrent:
         nprocs = PIPENV_MAX_SUBPROCESS
diff --git a/pipenv/resolver.py b/pipenv/resolver.py
index 733b28d5..b06deca6 100644
--- a/pipenv/resolver.py
+++ b/pipenv/resolver.py
@@ -504,55 +504,6 @@ class Entry(object):
         """
         if self.is_in_pipfile:
             return self.pipfile_entry.as_ireq()
-        return self.constraint_from_parent_conflicts()
-
-    def constraint_from_parent_conflicts(self):
-        """
-        Given a resolved entry with multiple parent dependencies with different
-        constraints, searches for the resolution that satisfies all of the parent
-        constraints.
-
-        :return: A new **InstallRequirement** satisfying all parent constraints
-        :raises: :exc:`~pipenv.exceptions.DependencyConflict` if resolution is impossible
-        """
-        # ensure that we satisfy the parent dependencies of this dep
-        parent_dependencies = set()
-        has_mismatch = False
-        can_use_original = True
-        for p in self.parent_deps:
-            # updated dependencies should be satisfied since they were resolved already
-            if p.is_updated:
-                continue
-            # parents with no requirements can't conflict
-            if not p.requirements:
-                continue
-            entry_ref = p.get_dependency(self.name)
-            required = entry_ref.get("required_version", "*")
-            required = self.clean_specifier(required)
-            parent_requires = self.make_requirement(self.name, required)
-            parent_dependencies.add("{0} => {1} ({2})".format(p.name, self.name, required))
-            # use pre=True here or else prereleases dont satisfy constraints
-            if parent_requires.requirement.specifier and (
-                not parent_requires.requirement.specifier.contains(self.original_version, prereleases=True)
-            ):
-                can_use_original = False
-            if parent_requires.requirement.specifier and (
-                not parent_requires.requirement.specifier.contains(self.updated_version, prereleases=True)
-            ):
-                if not self.entry.editable and self.updated_version != self.original_version:
-                    has_mismatch = True
-        if has_mismatch and not can_use_original:
-            from pipenv.exceptions import DependencyConflict
-            msg = (
-                "Cannot resolve {0} ({1}) due to conflicting parent dependencies: "
-                "\n\t{2}".format(
-                    self.name, self.updated_version, "\n\t".join(parent_dependencies)
-                )
-            )
-            raise DependencyConflict(msg)
-        elif can_use_original:
-            return self.lockfile_entry.as_ireq()
-        return self.entry.as_ireq()
 
     def validate_constraints(self):
         """
@@ -562,19 +513,24 @@ class Entry(object):
         :return: True if the constraints are satisfied by the resolution provided
         :raises: :exc:`pipenv.exceptions.DependencyConflict` if the constraints dont exist
         """
+        from pipenv.exceptions import DependencyConflict
+        from pipenv.environments import is_verbose
+
         constraints = self.get_constraints()
+        pinned_version = self.updated_version
         for constraint in constraints:
-            try:
-                constraint.check_if_exists(False)
-            except Exception:
-                from pipenv.exceptions import DependencyConflict
-                from pipenv.environments import is_verbose
+            if not constraint.req:
+                continue
+            if pinned_version and not constraint.req.specifier.contains(
+                str(pinned_version), prereleases=True
+            ):
                 if is_verbose():
                     print("Tried constraint: {0!r}".format(constraint), file=sys.stderr)
                 msg = (
                     "Cannot resolve conflicting version {0}{1} while {2}{3} is "
                     "locked.".format(
-                        self.name, self.updated_specifier, self.old_name, self.old_specifiers
+                        self.name, constraint.req.specifier,
+                        self.name, self.updated_specifier
                     )
                 )
                 raise DependencyConflict(msg)