There are reserved names in Windows/DOS, which can’t be used to name the user’s files.

For example: NUL, AUX, PRN, CON, LPT1, ...LPT9, etc.

Then, it is important to take into account this "restriction" when naming your objects, because a procedure named "RN" will generate a "PRN.PRG" file, which can’t be created because it is a reserved name.

The same occurs with the name of tables, indexes, etc. For example, if we call an AUX transaction the object will be TAUX.PRG but the base table’s name will be AUX, and in Fox it will be created a file named AUX.DBF

NOTE: some of the cases of reserved names are controlled by GeneXus ("illegal name" message).