A.24 library(lists): List Manipulation
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Availability::- use_module(library(lists)).(can be autoloaded)
Source[semidet]max_member(:Pred, -Max, +List)
True when Max is the largest member according to Pred, which must be a 2-argument callable that behaves like (@=<)/2. Fails if List is empty. The following call is equivalent to max_member/2: 
?- max_member(@=<, X, [6,1,8,4]).
X = 8.
See also
max_list/2 for the maximum of a list of numbers.