Evaluation

The top-level method of a Model instance is evaluate(), which assigns a semantic value to expressions of the logic module, under an assignment g:

>>> dom = val.domain
>>> g = nltk.sem.Assignment(dom)
>>> m.evaluate('all x.(boy(x) -> - girl(x))', g)
True

evaluate() calls a recursive function satisfy(), which in turn calls a function i() to interpret non-logical constants and individual variables. i() delegates the interpretation of these to the the model's Valuation and the variable assignment g respectively. Any atomic expression which cannot be assigned a value by i raises an Undefined exception; this is caught by evaluate, which returns the string 'Undefined'.

>>> m.evaluate('walk(adam)', g, trace=2)
<BLANKLINE>
'walk(adam)' is undefined under M, g
'Undefined'

Batch Processing

The utility functions interpret_sents() and evaluate_sents() are intended to help with processing multiple sentences. Here's an example of the first of these:

>>> sents = ['Mary walks']
>>> results = nltk.sem.util.interpret_sents(sents, 'grammars/sample_grammars/sem2.fcfg')
>>> for result in results:
...     for (synrep, semrep) in result:
...         print(synrep)
(S[SEM=<walk(mary)>]
  (NP[-LOC, NUM='sg', SEM=<\P.P(mary)>]
    (PropN[-LOC, NUM='sg', SEM=<\P.P(mary)>] Mary))
  (VP[NUM='sg', SEM=<\x.walk(x)>]
    (IV[NUM='sg', SEM=<\x.walk(x)>, TNS='pres'] walks)))

In order to provide backwards compatibility with 'legacy' grammars where the semantics value is specified with a lowercase sem feature, the relevant feature name can be passed to the function using the semkey parameter, as shown here:

>>> sents = ['raining']
>>> g = nltk.grammar.FeatureGrammar.fromstring("""
... % start S
... S[sem=<raining>] -> 'raining'
... """)
>>> results = nltk.sem.util.interpret_sents(sents, g, semkey='sem')
>>> for result in results:
...     for (synrep, semrep) in result:
...         print(semrep)
raining

The function evaluate_sents() works in a similar manner, but also needs to be passed a Model against which the semantic representations are evaluated.

Unit tests for relations and valuations

>>> from nltk.sem import *

Relations are sets of tuples, all of the same length.

>>> s1 = set([('d1', 'd2'), ('d1', 'd1'), ('d2', 'd1')])
>>> is_rel(s1)
True
>>> s2 = set([('d1', 'd2'), ('d1', 'd2'), ('d1',)])
>>> is_rel(s2)
Traceback (most recent call last):
  . . .
ValueError: Set set([('d1', 'd2'), ('d1',)]) contains sequences of different lengths
>>> s3 = set(['d1', 'd2'])
>>> is_rel(s3)
Traceback (most recent call last):
  . . .
ValueError: Set set(['d2', 'd1']) contains sequences of different lengths
>>> s4 = set2rel(s3)
>>> is_rel(s4)
True
>>> is_rel(set())
True
>>> null_binary_rel = set([(None, None)])
>>> is_rel(null_binary_rel)
True

Sets of entities are converted into sets of singleton tuples (containing strings).

>>> sorted(set2rel(s3))
[('d1',), ('d2',)]
>>> sorted(set2rel(set([1,3,5,])))
['1', '3', '5']
>>> set2rel(set()) == set()
True
>>> set2rel(set2rel(s3)) == set2rel(s3)
True

Predication is evaluated by set membership.

>>> ('d1', 'd2') in s1
True
>>> ('d2', 'd2') in s1
False
>>> ('d1',) in s1
False
>>> 'd2' in s1
False
>>> ('d1',) in s4
True
>>> ('d1',) in set()
False
>>> 'd1' in  null_binary_rel
False

>>> val = Valuation([('Fido', 'd1'), ('dog', set(['d1', 'd2'])), ('walk', set())])
>>> sorted(val['dog'])
[('d1',), ('d2',)]
>>> val.domain == set(['d1', 'd2'])
True
>>> print(val.symbols)
['Fido', 'dog', 'walk']

Parse a valuation from a string.

>>> v = """
... john => b1
... mary => g1
... suzie => g2
... fido => d1
... tess => d2
... noosa => n
... girl => {g1, g2}
... boy => {b1, b2}
... dog => {d1, d2}
... bark => {d1, d2}
... walk => {b1, g2, d1}
... chase => {(b1, g1), (b2, g1), (g1, d1), (g2, d2)}
... see => {(b1, g1), (b2, d2), (g1, b1),(d2, b1), (g2, n)}
... in => {(b1, n), (b2, n), (d2, n)}
... with => {(b1, g1), (g1, b1), (d1, b1), (b1, d1)}
... """
>>> val = Valuation.fromstring(v)

>>> print(val) # doctest: +SKIP
{'bark': set([('d1',), ('d2',)]),
 'boy': set([('b1',), ('b2',)]),
 'chase': set([('b1', 'g1'), ('g2', 'd2'), ('g1', 'd1'), ('b2', 'g1')]),
 'dog': set([('d1',), ('d2',)]),
 'fido': 'd1',
 'girl': set([('g2',), ('g1',)]),
 'in': set([('d2', 'n'), ('b1', 'n'), ('b2', 'n')]),
 'john': 'b1',
 'mary': 'g1',
 'noosa': 'n',
 'see': set([('b1', 'g1'), ('b2', 'd2'), ('d2', 'b1'), ('g2', 'n'), ('g1', 'b1')]),
 'suzie': 'g2',
 'tess': 'd2',
 'walk': set([('d1',), ('b1',), ('g2',)]),
 'with': set([('b1', 'g1'), ('d1', 'b1'), ('b1', 'd1'), ('g1', 'b1')])}

Unit tests for function argument application in a Model

>>> v = [('adam', 'b1'), ('betty', 'g1'), ('fido', 'd1'),\
...      ('girl', set(['g1', 'g2'])), ('boy', set(['b1', 'b2'])), ('dog', set(['d1'])),
...      ('love', set([('b1', 'g1'), ('b2', 'g2'), ('g1', 'b1'), ('g2', 'b1')])),
...      ('kiss', null_binary_rel)]
>>> val = Valuation(v)
>>> dom = val.domain
>>> m = Model(dom, val)
>>> g = Assignment(dom)
>>> sorted(val['boy'])
[('b1',), ('b2',)]
>>> ('b1',) in val['boy']
True
>>> ('g1',) in val['boy']
False
>>> ('foo',) in val['boy']
False
>>> ('b1', 'g1') in val['love']
True
>>> ('b1', 'b1') in val['kiss']
False
>>> sorted(val.domain)
['b1', 'b2', 'd1', 'g1', 'g2']

Propositional Model Test

>>> tests = [
...     ('P & Q', True),
...     ('P & R', False),
...     ('- P', False),
...     ('- R', True),
...     ('- - P', True),
...     ('- (P & R)', True),
...     ('P | R', True),
...     ('R | P', True),
...     ('R | R', False),
...     ('- P | R', False),
...     ('P | - P', True),
...     ('P -> Q', True),
...     ('P -> R', False),
...     ('R -> P', True),
...     ('P <-> P', True),
...     ('R <-> R', True),
...     ('P <-> R', False),
...     ]
>>> val1 = Valuation([('P', True), ('Q', True), ('R', False)])
>>> dom = set([])
>>> m = Model(dom, val1)
>>> g = Assignment(dom)
>>> for (sent, testvalue) in tests:
...     semvalue = m.evaluate(sent, g)
...     if semvalue == testvalue:
...         print('*', end=' ')
* * * * * * * * * * * * * * * * *

Test of i Function

>>> from nltk.sem import Expression
>>> v = [('adam', 'b1'), ('betty', 'g1'), ('fido', 'd1'),
...      ('girl', set(['g1', 'g2'])), ('boy', set(['b1', 'b2'])), ('dog', set(['d1'])),
...      ('love', set([('b1', 'g1'), ('b2', 'g2'), ('g1', 'b1'), ('g2', 'b1')]))]
>>> val = Valuation(v)
>>> dom = val.domain
>>> m = Model(dom, val)
>>> g = Assignment(dom, [('x', 'b1'), ('y', 'g2')])
>>> exprs = ['adam', 'girl', 'love', 'walks', 'x', 'y', 'z']
>>> parsed_exprs = [Expression.fromstring(e) for e in exprs]
>>> sorted_set = lambda x: sorted(x) if isinstance(x, set) else x
>>> for parsed in parsed_exprs:
...     try:
...         print("'%s' gets value %s" % (parsed, sorted_set(m.i(parsed, g))))
...     except Undefined:
...         print("'%s' is Undefined" % parsed)
'adam' gets value b1
'girl' gets value [('g1',), ('g2',)]
'love' gets value [('b1', 'g1'), ('b2', 'g2'), ('g1', 'b1'), ('g2', 'b1')]
'walks' is Undefined
'x' gets value b1
'y' gets value g2
'z' is Undefined

Test for formulas in Model

>>> tests = [
...     ('love(adam, betty)', True),
...     ('love(adam, sue)', 'Undefined'),
...     ('dog(fido)', True),
...     ('- dog(fido)', False),
...     ('- - dog(fido)', True),
...     ('- dog(sue)', 'Undefined'),
...     ('dog(fido) & boy(adam)', True),
...     ('- (dog(fido) & boy(adam))', False),
...     ('- dog(fido) & boy(adam)', False),
...     ('dog(fido) | boy(adam)', True),
...     ('- (dog(fido) | boy(adam))', False),
...     ('- dog(fido) | boy(adam)', True),
...     ('- dog(fido) | - boy(adam)', False),
...     ('dog(fido) -> boy(adam)', True),
...     ('- (dog(fido) -> boy(adam))', False),
...     ('- dog(fido) -> boy(adam)', True),
...     ('exists x . love(adam, x)', True),
...     ('all x . love(adam, x)', False),
...     ('fido = fido', True),
...     ('exists x . all y. love(x, y)', False),
...     ('exists x . (x = fido)', True),
...     ('all x . (dog(x) | - dog(x))', True),
...     ('adam = mia', 'Undefined'),
...     ('\\x. (boy(x) | girl(x))', {'g2': True, 'b2': True, 'b1': True, 'g1': True, 'd1': False}),
...     ('\\x. exists y. (boy(x) & love(x, y))', {'g2': False, 'b2': True, 'b1': True, 'g1': False, 'd1': False}),
...     ('exists z1. boy(z1)', True),
...     ('exists x. (boy(x) & - (x = adam))', True),
...     ('exists x. (boy(x) & all y. love(y, x))', False),
...     ('all x. (boy(x) | girl(x))', False),
...     ('all x. (girl(x) -> exists y. boy(y) & love(x, y))', False),
...     ('exists x. (boy(x) & all y. (girl(y) -> love(y, x)))', True),
...     ('exists x. (boy(x) & all y. (girl(y) -> love(x, y)))', False),
...     ('all x. (dog(x) -> - girl(x))', True),
...     ('exists x. exists y. (love(x, y) & love(x, y))', True),
...     ]
>>> for (sent, testvalue) in tests:
...     semvalue = m.evaluate(sent, g)
...     if semvalue == testvalue:
...         print('*', end=' ')
...     else:
...         print(sent, semvalue)
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

Satisfier Tests

>>> formulas = [
...     'boy(x)',
...     '(x = x)',
...     '(boy(x) | girl(x))',
...     '(boy(x) & girl(x))',
...     'love(adam, x)',
...     'love(x, adam)',
...     '- (x = adam)',
...     'exists z22. love(x, z22)',
...     'exists y. love(y, x)',
...     'all y. (girl(y) -> love(x, y))',
...     'all y. (girl(y) -> love(y, x))',
...     'all y. (girl(y) -> (boy(x) & love(y, x)))',
...     'boy(x) & all y. (girl(y) -> love(x, y))',
...     'boy(x) & all y. (girl(y) -> love(y, x))',
...     'boy(x) & exists y. (girl(y) & love(y, x))',
...     'girl(x) -> dog(x)',
...     'all y. (dog(y) -> (x = y))',
...     '- exists y. love(y, x)',
...     'exists y. (love(adam, y) & love(y, x))'
...     ]
>>> g.purge()
>>> g.add('x', 'b1')
{'x': 'b1'}
>>> for f in formulas: # doctest: +NORMALIZE_WHITESPACE
...     try:
...         print("'%s' gets value: %s" % (f, m.evaluate(f, g)))
...     except Undefined:
...         print("'%s' is Undefined" % f)
'boy(x)' gets value: True
'(x = x)' gets value: True
'(boy(x) | girl(x))' gets value: True
'(boy(x) & girl(x))' gets value: False
'love(adam, x)' gets value: False
'love(x, adam)' gets value: False
'- (x = adam)' gets value: False
'exists z22. love(x, z22)' gets value: True
'exists y. love(y, x)' gets value: True
'all y. (girl(y) -> love(x, y))' gets value: False
'all y. (girl(y) -> love(y, x))' gets value: True
'all y. (girl(y) -> (boy(x) & love(y, x)))' gets value: True
'boy(x) & all y. (girl(y) -> love(x, y))' gets value: False
'boy(x) & all y. (girl(y) -> love(y, x))' gets value: True
'boy(x) & exists y. (girl(y) & love(y, x))' gets value: True
'girl(x) -> dog(x)' gets value: True
'all y. (dog(y) -> (x = y))' gets value: False
'- exists y. love(y, x)' gets value: False
'exists y. (love(adam, y) & love(y, x))' gets value: True

>>> from nltk.sem import Expression
>>> for fmla in formulas: # doctest: +NORMALIZE_WHITESPACE
...     p = Expression.fromstring(fmla)
...     g.purge()
...     print("Satisfiers of '%s':\n\t%s" % (p, sorted(m.satisfiers(p, 'x', g))))
Satisfiers of 'boy(x)':
['b1', 'b2']
Satisfiers of '(x = x)':
['b1', 'b2', 'd1', 'g1', 'g2']
Satisfiers of '(boy(x) | girl(x))':
['b1', 'b2', 'g1', 'g2']
Satisfiers of '(boy(x) & girl(x))':
[]
Satisfiers of 'love(adam,x)':
['g1']
Satisfiers of 'love(x,adam)':
['g1', 'g2']
Satisfiers of '-(x = adam)':
['b2', 'd1', 'g1', 'g2']
Satisfiers of 'exists z22.love(x,z22)':
['b1', 'b2', 'g1', 'g2']
Satisfiers of 'exists y.love(y,x)':
['b1', 'g1', 'g2']
Satisfiers of 'all y.(girl(y) -> love(x,y))':
[]
Satisfiers of 'all y.(girl(y) -> love(y,x))':
['b1']
Satisfiers of 'all y.(girl(y) -> (boy(x) & love(y,x)))':
['b1']
Satisfiers of '(boy(x) & all y.(girl(y) -> love(x,y)))':
[]
Satisfiers of '(boy(x) & all y.(girl(y) -> love(y,x)))':
['b1']
Satisfiers of '(boy(x) & exists y.(girl(y) & love(y,x)))':
['b1']
Satisfiers of '(girl(x) -> dog(x))':
['b1', 'b2', 'd1']
Satisfiers of 'all y.(dog(y) -> (x = y))':
['d1']
Satisfiers of '-exists y.love(y,x)':
['b2', 'd1']
Satisfiers of 'exists y.(love(adam,y) & love(y,x))':
['b1']

Tests based on the Blackburn & Bos testsuite

>>> v1 = [('jules', 'd1'), ('vincent', 'd2'), ('pumpkin', 'd3'),
...       ('honey_bunny', 'd4'), ('yolanda', 'd5'),
...       ('customer', set(['d1', 'd2'])),
...       ('robber', set(['d3', 'd4'])),
...       ('love', set([('d3', 'd4')]))]
>>> val1 = Valuation(v1)
>>> dom1 = val1.domain
>>> m1 = Model(dom1, val1)
>>> g1 = Assignment(dom1)

>>> v2 = [('jules', 'd1'), ('vincent', 'd2'), ('pumpkin', 'd3'),
...       ('honey_bunny', 'd4'), ('yolanda', 'd4'),
...       ('customer', set(['d1', 'd2', 'd5', 'd6'])),
...       ('robber', set(['d3', 'd4'])),
...       ('love', set([(None, None)]))]
>>> val2 = Valuation(v2)
>>> dom2 = set(['d1', 'd2', 'd3', 'd4', 'd5', 'd6'])
>>> m2 = Model(dom2, val2)
>>> g2 = Assignment(dom2)
>>> g21 = Assignment(dom2)
>>> g21.add('y', 'd3')
{'y': 'd3'}

>>> v3 = [('mia', 'd1'), ('jody', 'd2'), ('jules', 'd3'),
...       ('vincent', 'd4'),
...       ('woman', set(['d1', 'd2'])), ('man', set(['d3', 'd4'])),
...       ('joke', set(['d5', 'd6'])), ('episode', set(['d7', 'd8'])),
...       ('in', set([('d5', 'd7'), ('d5', 'd8')])),
...       ('tell', set([('d1', 'd5'), ('d2', 'd6')]))]
>>> val3 = Valuation(v3)
>>> dom3 = set(['d1', 'd2', 'd3', 'd4', 'd5', 'd6', 'd7', 'd8'])
>>> m3 = Model(dom3, val3)
>>> g3 = Assignment(dom3)

>>> tests = [
...     ('exists x. robber(x)', m1, g1, True),
...     ('exists x. exists y. love(y, x)', m1, g1, True),
...     ('exists x0. exists x1. love(x1, x0)', m2, g2, False),
...     ('all x. all y. love(y, x)', m2, g2, False),
...     ('- (all x. all y. love(y, x))', m2, g2, True),
...     ('all x. all y. - love(y, x)', m2, g2, True),
...     ('yolanda = honey_bunny', m2, g2, True),
...     ('mia = honey_bunny', m2, g2, 'Undefined'),
...     ('- (yolanda = honey_bunny)', m2, g2, False),
...     ('- (mia = honey_bunny)', m2, g2, 'Undefined'),
...     ('all x. (robber(x) | customer(x))', m2, g2, True),
...     ('- (all x. (robber(x) | customer(x)))', m2, g2, False),
...     ('(robber(x) | customer(x))', m2, g2, 'Undefined'),
...     ('(robber(y) | customer(y))', m2, g21, True),
...     ('exists x. (man(x) & exists x. woman(x))', m3, g3, True),
...     ('exists x. (man(x) & exists x. woman(x))', m3, g3, True),
...     ('- exists x. woman(x)', m3, g3, False),
...     ('exists x. (tasty(x) & burger(x))', m3, g3, 'Undefined'),
...     ('- exists x. (tasty(x) & burger(x))', m3, g3, 'Undefined'),
...     ('exists x. (man(x) & - exists y. woman(y))', m3, g3, False),
...     ('exists x. (man(x) & - exists x. woman(x))', m3, g3, False),
...     ('exists x. (woman(x) & - exists x. customer(x))', m2, g2, 'Undefined'),
... ]

>>> for item in tests:
...     sentence, model, g, testvalue = item
...     semvalue = model.evaluate(sentence, g)
...     if semvalue == testvalue:
...         print('*', end=' ')
...     g.purge()
* * * * * * * * * * * * * * * * * * * * * *

Tests for mapping from syntax to semantics

Load a valuation from a file.

>>> import nltk.data
>>> from nltk.sem.util import parse_sents
>>> val = nltk.data.load('grammars/sample_grammars/valuation1.val')
>>> dom = val.domain
>>> m = Model(dom, val)
>>> g = Assignment(dom)
>>> gramfile = 'grammars/sample_grammars/sem2.fcfg'
>>> inputs = ['John sees a girl', 'every dog barks']
>>> parses = parse_sents(inputs, gramfile)
>>> for sent, trees in zip(inputs, parses):
...     print()
...     print("Sentence: %s" % sent)
...     for tree in trees:
...         print("Parse:\n %s" %tree)
...         print("Semantics: %s" %  root_semrep(tree))
<BLANKLINE>
Sentence: John sees a girl
Parse:
 (S[SEM=<exists x.(girl(x) & see(john,x))>]
  (NP[-LOC, NUM='sg', SEM=<\P.P(john)>]
    (PropN[-LOC, NUM='sg', SEM=<\P.P(john)>] John))
  (VP[NUM='sg', SEM=<\y.exists x.(girl(x) & see(y,x))>]
    (TV[NUM='sg', SEM=<\X y.X(\x.see(y,x))>, TNS='pres'] sees)
    (NP[NUM='sg', SEM=<\Q.exists x.(girl(x) & Q(x))>]
      (Det[NUM='sg', SEM=<\P Q.exists x.(P(x) & Q(x))>] a)
      (Nom[NUM='sg', SEM=<\x.girl(x)>]
        (N[NUM='sg', SEM=<\x.girl(x)>] girl)))))
Semantics: exists x.(girl(x) & see(john,x))
<BLANKLINE>
Sentence: every dog barks
Parse:
 (S[SEM=<all x.(dog(x) -> bark(x))>]
  (NP[NUM='sg', SEM=<\Q.all x.(dog(x) -> Q(x))>]
    (Det[NUM='sg', SEM=<\P Q.all x.(P(x) -> Q(x))>] every)
    (Nom[NUM='sg', SEM=<\x.dog(x)>]
      (N[NUM='sg', SEM=<\x.dog(x)>] dog)))
  (VP[NUM='sg', SEM=<\x.bark(x)>]
    (IV[NUM='sg', SEM=<\x.bark(x)>, TNS='pres'] barks)))
Semantics: all x.(dog(x) -> bark(x))

>>> sent = "every dog barks"
>>> result = nltk.sem.util.interpret_sents([sent], gramfile)[0]
>>> for (syntree, semrep) in result:
...     print(syntree)
...     print()
...     print(semrep)
(S[SEM=<all x.(dog(x) -> bark(x))>]
  (NP[NUM='sg', SEM=<\Q.all x.(dog(x) -> Q(x))>]
    (Det[NUM='sg', SEM=<\P Q.all x.(P(x) -> Q(x))>] every)
    (Nom[NUM='sg', SEM=<\x.dog(x)>]
      (N[NUM='sg', SEM=<\x.dog(x)>] dog)))
  (VP[NUM='sg', SEM=<\x.bark(x)>]
    (IV[NUM='sg', SEM=<\x.bark(x)>, TNS='pres'] barks)))
<BLANKLINE>
all x.(dog(x) -> bark(x))

>>> result = nltk.sem.util.evaluate_sents([sent], gramfile, m, g)[0]
>>> for (syntree, semrel, value) in result:
...     print(syntree)
...     print()
...     print(semrep)
...     print()
...     print(value)
(S[SEM=<all x.(dog(x) -> bark(x))>]
  (NP[NUM='sg', SEM=<\Q.all x.(dog(x) -> Q(x))>]
    (Det[NUM='sg', SEM=<\P Q.all x.(P(x) -> Q(x))>] every)
    (Nom[NUM='sg', SEM=<\x.dog(x)>]
      (N[NUM='sg', SEM=<\x.dog(x)>] dog)))
  (VP[NUM='sg', SEM=<\x.bark(x)>]
    (IV[NUM='sg', SEM=<\x.bark(x)>, TNS='pres'] barks)))
<BLANKLINE>
all x.(dog(x) -> bark(x))
<BLANKLINE>
True

>>> sents = ['Mary walks', 'John sees a dog']
>>> results = nltk.sem.util.interpret_sents(sents, 'grammars/sample_grammars/sem2.fcfg')
>>> for result in results:
...     for (synrep, semrep) in result:
...         print(synrep)
(S[SEM=<walk(mary)>]
  (NP[-LOC, NUM='sg', SEM=<\P.P(mary)>]
    (PropN[-LOC, NUM='sg', SEM=<\P.P(mary)>] Mary))
  (VP[NUM='sg', SEM=<\x.walk(x)>]
    (IV[NUM='sg', SEM=<\x.walk(x)>, TNS='pres'] walks)))
(S[SEM=<exists x.(dog(x) & see(john,x))>]
  (NP[-LOC, NUM='sg', SEM=<\P.P(john)>]
    (PropN[-LOC, NUM='sg', SEM=<\P.P(john)>] John))
  (VP[NUM='sg', SEM=<\y.exists x.(dog(x) & see(y,x))>]
    (TV[NUM='sg', SEM=<\X y.X(\x.see(y,x))>, TNS='pres'] sees)
    (NP[NUM='sg', SEM=<\Q.exists x.(dog(x) & Q(x))>]
      (Det[NUM='sg', SEM=<\P Q.exists x.(P(x) & Q(x))>] a)
      (Nom[NUM='sg', SEM=<\x.dog(x)>]
        (N[NUM='sg', SEM=<\x.dog(x)>] dog)))))

Cooper Storage

>>> from nltk.sem import cooper_storage as cs
>>> sentence = 'every girl chases a dog'
>>> trees = cs.parse_with_bindops(sentence, grammar='grammars/book_grammars/storage.fcfg')
>>> semrep = trees[0].label()['SEM']
>>> cs_semrep = cs.CooperStore(semrep)
>>> print(cs_semrep.core)
chase(z2,z4)
>>> for bo in cs_semrep.store:
...     print(bo)
bo(\P.all x.(girl(x) -> P(x)),z2)
bo(\P.exists x.(dog(x) & P(x)),z4)
>>> cs_semrep.s_retrieve(trace=True)
Permutation 1
   (\P.all x.(girl(x) -> P(x)))(\z2.chase(z2,z4))
   (\P.exists x.(dog(x) & P(x)))(\z4.all x.(girl(x) -> chase(x,z4)))
Permutation 2
   (\P.exists x.(dog(x) & P(x)))(\z4.chase(z2,z4))
   (\P.all x.(girl(x) -> P(x)))(\z2.exists x.(dog(x) & chase(z2,x)))

>>> for reading in cs_semrep.readings:
...     print(reading)
exists x.(dog(x) & all z3.(girl(z3) -> chase(z3,x)))
all x.(girl(x) -> exists z4.(dog(z4) & chase(x,z4)))