I have two columns of data that represent days of the week. One column holds all the possible days of the week that a route can be run such as "MTRFS" or "MTWRF." The other column includes days that a route cannot run such as "TFS" or "M." I am trying to come up with another column that will subtract the cell from the days that a route cannot run column from a cell in the possible days column. Is it possible to subtract one string from another like this?