I am new to prolog.
I read this article about structures in Prolog. However, the following code does not work:

is_point(point1,point(5,7)).


test0:-is_point(point1,X),test1(X).
test1(X):X=point(OX,OY),OX=5.
test2:-test1(point(5,8)).

somepoints([ point(5,6), point(5,10)]).
test3:-somepoints(L),L is [X|_],test1(X).

The query ? is_point(point1,X). does work. Also ? some_points(L). but launching ? test0., ? test2. or test3. gives approximately the same error, which is

14 ?- test0.
ERROR: Unknown procedure: test1/1
ERROR:   However, there are definitions for:
ERROR:         test0/0
ERROR:         test2/0
ERROR:         test3/0
ERROR: 
ERROR: In:
ERROR:   [13] test1(point(5,7))
ERROR:   [11] toplevel_call(user:user:test0) at c:/software/msys64/mingw64/lib/swipl/boot/toplevel.pl:1317
ERROR: 
ERROR: Note: some frames are missing due to last-call optimization.
ERROR: Re-run your program in debug mode (:- debug.) to get more detail.
   Exception: (13) 
    [[ EXCEPTION while printing message '~W'
       with arguments [test1(point(5,7)),[max_depth(3.4848e-319),quoted(true),portray(true),attributes(portray),spacing(next_argument)]]:
       raised: type_error(integer,3.4848e-319)
    ]]

So what is the correct syntax to work with structures in Prolog?