There is an interesting feature offered by latex: typographical ligatures. A german example for double and even tripple f’s would be: Schiff (ship) or Sauerstoffflasche (oxygen tank). Where the German orthography prohibits ligature across two syllables. So it would be wrong to apply the ligature for the tripple f on Schifffahrt (shipping).
In Latex the ligature is applied automatically for every double f (or ffl or fl), but you can avoid this via \/ or |.
Look at the following picture and see the ‘ligatured’ letters on the left and letters with standard typography on the right side:
Here is the latex code:
ffl ff\/l \\ ff f\/f \\ fl f\/l