saul:/home/dale/classes/360 1> elp
Standard ML of New Jersey, Version 0.93, February 15, 1993
Elp, Version 0.1x, Built: Fri Jan  7 12:41:04 EST 1994
?- load "path".
[reading file ./path.mod]
node : type.
adj : node -> node -> node.
path : node -> node -> node.
a : node.
b : node.
c : node.
d : node.
e : node.
f : node.
[closed file ./path.mod]
path:14.1-14.8 Error: Type checking failed
adj a b  : node <> o
Unification failure due to clash: o <> node

std_in:14.1-14.8 Error: Type checking failed
adj a b  : node <> o
Unification failure due to clash: o <> node

caught exception TypeCheckFail

?- load "path".
[reading file ./path.mod]
node : type.
adj : node -> node -> o.
path : node -> node -> o.
a : node.
b : node.
c : node.
d : node.
e : node.
f : node.
[closed file ./path.mod]
solved

yes
?-

?- path b d.
std_in:1.2-1.6 Error: Undeclared constant path
caught exception UndeclConst
?- use "path".
?- path b d.
solved

yes
?- path b X.
X = c.
;
X = d.
;
no more solutions
?- path X Y.
Y = b,
X = a.
;
Y = c,
X = a.
;
Y = c,
X = b.
;
Y = d,
X = c.
;
Y = d,
X = e.
;
Y = c,
X = a.
;
Y = d,
X = a.
;
Y = d,
X = a.
;
Y = d,
X = b.
;
no more solutions
?-