def test_walk2():
v, w, x, y = variables("v, w, x, y")
substitution = Substitution({x: y, v: x, w: x})
assert substitution.walk(x) is y
assert substitution.walk(v) is y
assert substitution.walk(w) is y
def test_walk1():
a, w, x, y, z = variables("a, w, x, y, z")
substitution = Substitution({z: a, x: w, y: z})
assert substitution.walk(x) is w
assert substitution.walk(y) is a
assert substitution.walk(z) is a
def test_extend_and_walk():
x, y, z = variables("x, y, z")
s = Substitution({z: x, y: z})
s = s.extend(x, 'e')
assert s.walk(y) == 'e'
def test_walk3():
b, v, w, x, y, z = variables("b, v, w, x, y, z")
substitution = Substitution({x: b, z: y, w: (x, "e", z)})
assert substitution.walk(w) == (x, "e", z)
