Problem Statement

The use of   abbreviations   (also sometimes called synonyms, nicknames, AKAs, or aliases)   can be an easy way to add flexibility when specifying or using commands, sub─commands, options, etc.

It would make a list of words easier to maintain   (as words are added, changed, and/or deleted)   if the minimum abbreviation length of that list could be automatically (programmatically) determined.

For this task, use the list (below) of the days-of-the-week names that are expressed in about a hundred languages   (note that there is a blank line in the list). Caveat:   The list (above) most surely contains errors (or, at the least, differences) of what the actual (or true) names for the days-of-the-week.

To make this Rosetta Code task page as small as possible, if processing the complete list, read the days-of-the-week from a file (that is created from the above list).

Notes concerning the above list of words

Let's start with the solution:

let fN g=let rec fN n=if g|>List.map(fun(g:string)->g.[0..n])|>Set.ofList|>Set.count=(List.length g) then (n+1) else fN(n+1)
         fN 0


fN ["Sunday"; "Monday"; "Tuesday"; "Wednesday"; "Thursday"; "Friday"; "Saturday"]                  // -> 2
fN ["Sondag"; "Maandag"; "Dinsdag"; "Woensdag"; "Donderdag"; "Vrydag"; "Saterdag"]                 // -> 2
fN ["E_djelë"; "E_hënë"; "E_martë"; "E_mërkurë"; "E_enjte"; "E_premte"; "E_shtunë"]                // -> 4
fN ["Ehud"; "Segno"; "Maksegno"; "Erob"; "Hamus"; "Arbe"; "Kedame"]                                // -> 2
fN ["Al_Ahad"; "Al_Ithinin"; "Al_Tholatha'a"; "Al_Arbia'a"; "Al_Kamis"; "Al_Gomia'a"; "Al_Sabit";] // -> 5