listing function ls()
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To list all variable for functions, we use the ls()

Example #1: Assume that we have nothing, see below. 

    > ls()
      character(0)
    >

Example #2: 

    > pv<-100
    > r<-0.1
    > n<-5
    > ls()
        [1] "n"  "pv" "r" 
    > 

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Assigning a value without defining it first 
///////////////////////////////
For many programming languages, programmers have to define a variable first. 
For R, we could simply assign a value, such 
   x=100
   y=500

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remove a variable or several variables
////////////////////////////////

 1) To remove a variable, we use the rm() function 

    >rm(pv)

 2) To remove two variables such as pv and r, 

    >rm(pv,r)

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Videos
///////////////////////////////////////////////////////////////////////////////
 Kirbyson,Brie, 2023, The Perfect ChatGPT Prompt Formula (Start With This!) 
   (t13:02,v26k,s29.1k)
   https://www.youtube.com/watch?v=e7d4HMPs2fs

 Skill Leap AI, 2023, I Discovered The Perfect ChatGPT Prompt Formula
    (t6:26, s94.5k)
    https://www.youtube.com/watch?v=pmzZF2EnKaA

 Su, Jeff, 2023, Master the Perfect ChatGPT Prompt Formula (in just 8 minutes)!
   (t8:29,v729k,s659k)
   https://www.youtube.com/watch?v=jC4v5AS4RIM
///////////////////////////////////////////////////////////////////////////////

Upper-arrow and down-arrow keys 
///////////////////////////////
  We typing commands, we can use the up-arrow key to recall 
     the previous commands. 

  Thus, by using the up-arrow and down-arrow keys, we 
    can save some of our typing time
 
/////////////////////////////////

One benefit of -> assignment 
///////////////////////////////
 Assume we type the following 

  100*(1+0.1)^2

  If we want to assign the above result to a value,
    we can use the upper-arrow key to recall the 
    command, then add ->a, shown below. 

  100*(1+0.1)^2 ->a

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