% NehcihsahA (Omaha style)
mother(x,y).
mother(y,z).
mother(zz,z).
sex(zz,male).
sister(z,zzz).
mother(z4,zzz).
sex(z4,male).
father(z,a).
sister(a,b).
mother(c,b).
sex(c,male).
brother(y,yy).
father(y1,yy).
father(y2,y1).
sister(b,d).
father(y3,y2).
sex(y3,female).