:- use_module(library(chr)).
:- chr_constraint is_true/1.
:- initialization(main).

is_true([A,means,B]) ==> (is_true(A) ==> is_true(B)).
is_true([[A,is,true],means,[A,is,not,false]]).
is_true([something,is,true]).

?- is_true([something,is,true]).
true .

?- is_true([something,is,not,false]).
is_true([something, is, not, false]).