
  -spec multiple_relative_product(TupleOfBinRels, BinRel1) -> BinRel2
                                     when
                                         TupleOfBinRels ::
                                             tuple_of(BinRel),
                                         BinRel :: binary_relation(),
                                         BinRel1 :: binary_relation(),
                                         BinRel2 :: binary_relation().

  If TupleOfBinRels is a non-empty tuple {R[1], ..., R[n]} of
  binary relations and BinRel1 is a binary relation, then BinRel2
  is the multiple relative product of the ordered set
  (R[i], ..., R[n]) and BinRel1.

    1> Ri = sofs:relation([{a,1},{b,2},{c,3}]),
    R = sofs:relation([{a,b},{b,c},{c,a}]),
    MP = sofs:multiple_relative_product({Ri, Ri}, R),
    sofs:to_external(sofs:range(MP)).
    [{1,2},{2,3},{3,1}]
