%% %CopyrightBegin%
%%
%% SPDX-License-Identifier: Apache-2.0
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[;1m  family_intersection(Family1, Family2)[0m

  If [;;4mFamily1[0m and [;;4mFamily2[0m are families, then [;;4mFamily3[0m is the
  family such that the index set is the intersection of [;;4mFamily1[0m:s
  and [;;4mFamily2[0m:s index sets, and [;;4mFamily3[0m[i] is the intersection
  of [;;4mFamily1[0m[i] and [;;4mFamily2[0m[i].

[;1mExamples[0m

    1> F1 = sofs:family([{a,[1,2]},{b,[3,4]},{c,[5,6]}]).
    2> F2 = sofs:family([{b,[4,5]},{c,[7,8]},{d,[9,10]}]).
    3> F3 = sofs:family_intersection(F1, F2).
    4> sofs:to_external(F3).
    [{b,[4]},{c,[]}]
