% SUCCESS: X is unified with the constant hans
X = hans.

% FAILURE: two different constants cannot be unified
anja = hans.

% SUCCESS: the first line unifies the variable X with hans,
% and the second Y with X, i.e., with hans.
X = hans,
X = Y.

% SUCCESS: the variable X is unified with the predicate
% happy(hans)
X = happy(hans).

% FAILURE: Y is undefined.
X is Y.

% FAILURE: The predicate 2+1 cannot be unified with 3, unless
% the arithmetic expression is reduced
2+1 = 3.

% SUCCESS: The variable X is unified with the constant a
f(X,a) = f(a,X).

% FAILURE: X cannot be unified with anja and with hans at the
% same time
likes(anja, X) = likes(X, hans).

% SUCCESS: The variable A is unified with the predicate b(c)
A = b(c).

% FAILURE: a constant cannot be unified to another constant
% (in this case, a predicate).
a = b(c).
