UnionBlist( blist1, blist2.. ) 
UnionBlist( list )
In the  first form UnionBlist  returns the union  of the  boolean lists
blist1, blist2, etc., which must have equal length.  The union is a
new boolean list such that union[i] = blist1[i] or blist2[i]
or ...
In  the second form  list must  be a  list  of boolean lists  blist1,
blist2, etc.,  which  must have  equal length,  and Union returns the
union of those boolean list.
    gap> blist1 := [ true, true, false, false ];;
    gap> blist2 := [ true, false, true, false ];;
    gap> UnionBlist( blist1, blist2 );
    [ true, true, true, false ] 
Note  that UnionBlist  is  implemented   in terms  of    the  procedure
UniteBlist (see UniteBlist).
GAP 3.4.4