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%% SPDX-License-Identifier: Apache-2.0
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[;1m  is_a_function(BinRel)[0m

  Returns [;;4mtrue[0m if the binary relation [;;4mBinRel[0m is a function or
  the untyped empty set; otherwise, returns [;;4mfalse[0m.

[;1mExamples[0m

    1> sofs:is_a_function(sofs:relation([{1,a},{2,b},{3,c}])).
    true
    2> sofs:is_a_function(sofs:relation([{1,a},{1,b},{3,c}])).
    false
    3> sofs:is_a_function(sofs:set([a,b,c])).
    ** exception error: bad argument
         in function  sofs:is_a_function/1
