diff --git a/slide_r_elements_1.Rmd b/slide_r_elements_1.Rmd
index 7eaeeb7..e48acec 100644
--- a/slide_r_elements_1.Rmd
+++ b/slide_r_elements_1.Rmd
@@ -363,7 +363,7 @@ number <- 3.14
 number.text <- as.character(number) # cast to char
 number.text
 class(number.text)
-as.numeric(number.text) # and the other way round
+as.numeric(number.text) # and the other way around
 ```
 
 ---
diff --git a/slide_r_environment.Rmd b/slide_r_environment.Rmd
index 968b28d..c95ea84 100644
--- a/slide_r_environment.Rmd
+++ b/slide_r_environment.Rmd
@@ -119,7 +119,7 @@ We also have [GitHub](https://github.com).
 --
 # Working with packages -- CRAN example.
 
-```{r,out.width="100%",fig.align='center',echo=FALSE}
+```{r,out.width="80%",fig.align='center',echo=FALSE}
 knitr::include_graphics("data/slide_r_environment/ggplot2_CRAN.png")
 ```
 
@@ -166,7 +166,6 @@ name: source_pkg_inst
 
 # Working with packages -- installing from source.
 
-- Make sure you have appropriate tools installed, e.g. XCode or build-essentials.
 - Download the source file, in our example *ggplot2_3.4.3.tar.gz*.
 - Install it:
 
@@ -191,7 +190,7 @@ name: pkg_github
 
 # Packages -- GitHub
 
-Nowadays, more and more developers contribute their packages via GitHub. The easiest way to install packages from the GitHub is via the *devtools* package:
+Nowadays, more and more developers distribute their packages via GitHub. The easiest way to install packages from the GitHub is via the *devtools* package:
 
 - Install the *devtools* package.
 - Load it.
diff --git a/slide_r_programming_1.Rmd b/slide_r_programming_1.Rmd
index c007478..1cfd08c 100644
--- a/slide_r_programming_1.Rmd
+++ b/slide_r_programming_1.Rmd
@@ -37,7 +37,10 @@ count: false
 ---
 name: programming_language
 
-# Computer program
+# Programing Language    
+
+--
+> Programming is a process of instructing a computer to perform a specific task. We write these instructions by **programming language**. It can be as simple as calculation (like a calculator) or complex applications. 
 
 --
 
@@ -69,11 +72,7 @@ name: programming_language
    * For example `mean()`, `min()`   
 --
 
-# How?
 
---
-> A **programming language** is a formal computer language or constructed language designed to communicate instructions to a machine, particularly a computer. Programming languages can be used to create programs to control the behavior of a machine or to express algorithms.  
-.small[[Wikipedia](https://en.wikipedia.org/wiki/Programming_language)]
 
 ---
 
@@ -102,7 +101,7 @@ name: programming_language
 
   * int &mdash; 1 2 5 9
   * double &mdash; 1.23 -5.74
-  * char &mdash; a b test 7 9
+  * char &mdash; a b test 
 
 --
 
@@ -144,7 +143,7 @@ count: false
 
 ```{r,include=FALSE,eval=FALSE}
 # manually run this to render this document to HTML
-rmarkdown::render("presentation_demo.Rmd")
+#rmarkdown::render("presentation_demo.Rmd")
 # manually run this to convert HTML to PDF
 #pagedown::chrome_print("presentation_demo.html",output="presentation_demo.pdf")
 ```