A.8.17.4 Global constraints
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all_distinct(+Vars)
True iff Vars are pairwise distinct. For example, all_distinct/1 can detect that not all variables can assume distinct values given the following domains: 
?- maplist(in, Vs,
           [1\/3..4, 1..2\/4, 1..2\/4, 1..3, 1..3, 1..6]),
   all_distinct(Vs).
false.
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