Day: 13 July 2016

1. or: returns true if an argument is true
   or(logical value 1, logical value 2, …)
2. isna: returns true if value equals #N/A
   isna(value)
3. isblank: returns true if value refers to an empty cell
   isblank(value)
4. not: reverses the value of the argument
   not(logical value)
5. na: not available. returns the error value #N/A
   na()