diff --git a/.circleci/config.yml b/.circleci/config.yml
index 6e07ce3..450f444 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -21,16 +21,6 @@ shared: &shared
 
 
 jobs:
-  py36:
-    <<: *shared
-    docker:
-      - image: cimg/python:3.6
-
-  py37:
-    <<: *shared
-    docker:
-      - image: cimg/python:3.7
-
   py38:
     <<: *shared
     docker:
@@ -56,8 +46,6 @@ workflows:
   version: 2
   build:
     jobs:
-      - py36
-      - py37
       - py38
       - py39
       - py310
diff --git a/.readthedocs.yaml b/.readthedocs.yaml
index 2de0eb9..9e45017 100644
--- a/.readthedocs.yaml
+++ b/.readthedocs.yaml
@@ -9,6 +9,11 @@ version: 2
 sphinx:
   configuration: docs/conf.py
 
+build:
+  os: ubuntu-22.04
+  tools:
+    python: "3.8"
+
 # Build documentation with MkDocs
 #mkdocs:
 #  configuration: mkdocs.yml
@@ -18,8 +23,5 @@ formats: all
 
 # Optionally set the version of Python and requirements required to build your docs
 python:
-  version: 3.8
   install:
-    - requirements: requirements.txt
-    - method: pip
-      path: .
+    - requirements: docs/requirements.txt
diff --git a/README.md b/README.md
index f00c2af..a9d7dde 100644
--- a/README.md
+++ b/README.md
@@ -39,17 +39,14 @@ the codes of TDA separately, and name this package `mogutda`.
 
 ## Prerequisite
 
-It runs under Python 3.6, 3.7, 3.8, 3.9, 3.10, and 3.11.
-
-Release 0.1.5 can work under `numpy`>0.16.0, but previous
-release will constitute error under the new `numpy`.
+It runs under Python 3.8, 3.9, 3.10, and 3.11.
 
 ## Simple Tutorial: Simplicial Complex
 
 You can install by:
 
 ```
-pip install -U mogutda
+pip install mogutda
 ```
 
 To establish a simplicial complex for a torus, type
@@ -93,6 +90,7 @@ the simplicial complexes are, and how homologies are defined:
 
 ## News
 
+* 08/18/2023: `mogutda` 0.4.0 released.
 * 06/20/2023: `mogutda` 0.3.5 released.
 * 09/09/2022: `mogutda` 0.3.4 released.
 * 07/15/2021: `mogutda` 0.3.3 released.
diff --git a/docs/conf.py b/docs/conf.py
index ea18788..1b75dcc 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -60,7 +60,7 @@
 # The short X.Y version.
 version = u'0.3'
 # The full version, including alpha/beta/rc tags.
-release = u'0.3.5'
+release = u'0.4.0'
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.
diff --git a/docs/index.rst b/docs/index.rst
index b578e07..09c480c 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -16,7 +16,7 @@ draw some insights from them. A lot of machine learning algorithms deal
 with distances, which are extremely useful, but they miss the
 information the data may carry from their geometry.
 
-`mogutda` runs in Python 3.6, 3.7, 3.8, 3.9, 3.10, and 3.11.
+`mogutda` runs in Python 3.8, 3.9, 3.10, and 3.11.
 
 Contributors:
 
diff --git a/docs/news.rst b/docs/news.rst
index 37312e8..d444a48 100644
--- a/docs/news.rst
+++ b/docs/news.rst
@@ -1,6 +1,7 @@
 News
 ====
 
+* 08/18/2023: `mogutda` 0.4.0 released.
 * 06/20/2023: `mogutda` 0.3.5 released.
 * 09/09/2022: `mogutda` 0.3.4 released.
 * 07/15/2021: `mogutda` 0.3.3 released.
diff --git a/docs/requirements.txt b/docs/requirements.txt
new file mode 100644
index 0000000..dfe6a35
--- /dev/null
+++ b/docs/requirements.txt
@@ -0,0 +1,4 @@
+numpy==1.23.3
+scipy==1.10.0
+networkx==3.1
+matplotlib==3.3.0
diff --git a/requirements.txt b/requirements.txt
index 7ecb2b9..972a315 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +1,4 @@
 numpy>=1.16.0
-scipy>=1.2.0
+scipy>=1.10.0
 networkx>=2.0
 matplotlib>=3.3.0
diff --git a/setup.py b/setup.py
index 4e217d0..5fcf85f 100644
--- a/setup.py
+++ b/setup.py
@@ -21,15 +21,13 @@ def install_requirements():
 
 
 setup(name='mogutda',
-      version="0.3.5",
+      version="0.4.0",
       description="Topological Data Analysis in Python",
       long_description=package_description(),
       long_description_content_type='text/markdown',
       classifiers=[
           "Topic :: Scientific/Engineering :: Mathematics",
           "Topic :: Scientific/Engineering :: Physics",
-          "Programming Language :: Python :: 3.6",
-          "Programming Language :: Python :: 3.7",
           "Programming Language :: Python :: 3.8",
           "Programming Language :: Python :: 3.9",
           "Programming Language :: Python :: 3.10",