MS Word: word documents vs. text files
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1) Generate a Word document
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   Launch MS Word and type the following two lines

   pv<-100
   r<-0.1

  c) Save it as test.docx under your current working directory
  d) source('test.docx')

2) Generate a text file
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  a) Launch MS Word and type the following two lines
     pv<-100
     r<-0.1
  c) Save as, then choose 'Plain text'
     Save it under your current working directory as test.txt
  d) rm(list=ls())     # 
  e) source('test.txt')
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Issues with the IRR rule
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For a normal project defined as cash outflows occurring before any cash inflows, 
   the NPV and IRR rules usually offer the same conclusions. For abnormal projects,
   where some cash inflows are followed by cash outflows, the NPV and IRR rules 
   might offer conflicting findings. When the future cash flows change signs n 
   times, we might end up with different IRR estimates. 

There are several reasons why the NPV rule is preferred to the IRR rule. First,
    there might be no IRR that makes NPV equal to zero, i.e., we fail to find 
    any IRR. Second, there might be multiple IRRs. This is true when the future
    cash flows change signs more than once. In other words, we might find two IRRs,
    9% and 14%. If our cost of capital is 10%, we cannot apply the IRR rule to decide
    whether to choose or reject the project. Third, the reinvestment rate assumption 
    underlying the IRR rule is unrealistic. For those cases, the NPV rule dominates the IRR rule. 

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How to use .existRemoteFile (.is404) and .codeImage (.ci)
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Function 1: .existRemoteFile
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             short-cut name is .is404
             Type the function name to see its usage 

Function 2:  .codeImage
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             short-cut is .ci
             Type the function name to see its usage 

             Compare the following three lines
             .ci('pv_f')      # all functions contain 'pv_f'
             .ci('pv_f.*R')   # functions contain 'pv_f' and 'R' plus anything between
                                .* means anything 
             .ci('pv_f.*R$')  # same as the above except R is the last letter
                                $ indicates the last one
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