Telephone Conversation Logic Puzzle {Prolog} -

year('1928'). year('1929'). year('1932'). year('1935').  person(gertie). person(herbert). person(miriam). person(wallace).  exchange(al). exchange(be). exchange(pe). exchange(sl).  solve:- year(y1), year(y2), year(y3), year(y4),         unique([y1,y2,y3,y4]),      exchange(gertex), exchange(herbex), exchange(mirex), exchange(wallex),     unique([gertex,herbex,mirex,wallex]),      triples= [[gertie,y1,gertex],           [herbert,y2,herbex],           [miriam,y3,mirex],           [wallace,y4,wallex]],     %herberts first exchange     \+ member([herbert,be,_],triples),     %neither herberts nor gerties first exchange sl     \+ (         member([herbert,sl,_],triples);         member([gertie,sl,_],triples)         ),     %the exchange wasnt made in 1935     \+ member([_,be,'1935'],triples),     %neither al nor exchanges made in 1932     \+ (          member([_,al,'1932'],triples);          member([_,be,'1932'],triples)        ),     %the pe exchange made in 1929        member([_,pe,'1929'],triples),     %wallace's first exchange al        member([wallace,al,_],triples),         writer(gertie,y1,gertex),        writer(herbert,y2,herbex),        writer(miriam,y3,mirex),        writer(wallace,y4,wallex).  writer(x,y,z):- write(x), write(' made '), write(y), write(' exchange in '), write(z), nl.  unique([h | t]) :- member(h, t), !, fail. unique([_ | t]) :- unique(t). unique([_]). 

i try run returns false statement. got question http://www.cis.upenn.edu/~matuszek/cis554-2012/assignments/prolog-01-logic-puzzle.html , can see it's same it's-a-tie.pl sample apart of atoms used , of logic involved...anybody have idea i'm doing wrong?

seems there swapped fields. changing triples this

triples= [[gertie,gertex,y1],       [herbert,herbex,y2],       [miriam,mirex,y3],       [wallace,wallex,y4]], 

i get

?- solve. gertie made 1928 exchange in herbert made 1929 exchange in pe miriam made 1932 exchange in sl wallace made 1935 exchange in al true .