Variable names and procedure names are not allowed to include spaces. Instead of a blank character you should use the underscore "_" for improving the readability of long variable names. Upper case and lower case letters are distinct, so x and X are two different names. Although keywords like IF, THEN, LOOP, etc., are not reserved words and would be correct names for variables and procedures, it is not very useful to use such keywords as names. It would be convenient to choose names that are related to the purpose of the variable or procedure. The actual implementation allows names to have a maximum length of 80 characters.