
[;1m  family_range(Family1)[0m

  If [;;4mFamily1[0m is a family and [;;4mFamily1[0m[i] is a binary relation for
  every i in the index set of [;;4mFamily1[0m, then [;;4mFamily2[0m is the
  family with the same index set as [;;4mFamily1[0m such that [;;4mFamily2[0m[i]
  is the range of [;;4mFamily1[0m[i].

    1> FR = sofs:from_term([{a,[{1,a},{2,b},{3,c}]},{b,[]},{c,[{4,d},{5,e}]}]),
    F = sofs:family_range(FR),
    sofs:to_external(F).
    [{a,[a,b,c]},{b,[]},{c,[d,e]}]
