I had a strange error when using the variable x and was about to ask if
there was a bug in obsubst...
(%i1) load(opsubst);
(%o1)
C:/Programme/Maxima-5.17.1/share/maxima/5.17.1/share/contrib/gentran/test/T.mac
(%i2) values;
(%o2) [x,t]
(%i3) x;
(%o3) y+t
(%i4) t;
(%o4) y
... then I discovered that the manual suggested to
(%i5) load("opsubst");
(%o5)
C:/Programme/Maxima-5.17.1/share/maxima/5.17.1/share/contrib/opsubst.lisp
and that in the first case, the wrong file was loaded (why?). In other
places however, the manual suggests to load packages without double
quotes (e.g. load(itensor)) - thats why I should "be wary of the trap!".