predicates.proofs module¶
Schemas and proofs in Predicate Logic.

predicates.proofs.
InstantiationMap
¶ A mapping from constant names, variable names, and relation names to terms, variable names, and formulas respectively.
alias of Mapping[str, Union[predicates.syntax.Term, str, predicates.syntax.Formula]]

class
predicates.proofs.
Schema
(formula, templates=frozenset({}))¶ Bases:
object
An immutable schema of predicatelogic formulas, comprised of a formula along with the constant names, variable names, and nullary or unary relation names in that formula that serve as templates. A template constant name is a placeholder for any term. A template variable name is a placeholder for any variable name. A template nullary or unary relation name is a placeholder for any (parametrized for a unary relation name) predicatelogic formula that does not refer to any variable name in the schema (except possibly through its instantiated parameter for a unary relation name).
 Variables

__init__
(formula, templates=frozenset({}))¶ Initializes a
Schema
from its formula and template names. Parameters
formula (
Formula
) – the formula for the schema.templates (
AbstractSet
[str
]) – the constant, variable, and relation names from the formula to serve as templates.

__repr__
()¶ Computes a string representation of the current schema.
 Return type
 Returns
A string representation of the current schema.

__eq__
(other)¶ Compares the current schema with the given one.

__ne__
(other)¶ Compares the current schema with the given one.

exception
BoundVariableError
(variable_name, relation_name)¶ Bases:
Exception
Raised by
_instantiate_helper
when a variable name becomes bound during a schema instantiation in a way that is disallowed in that context. Variables

__init__
(variable_name, relation_name)¶ Initializes a
BoundVariableError
from the offending variable name and the relation name during whose substitution the error occurred.

static
_instantiate_helper
(formula, constants_and_variables_instantiation_map, relations_instantiation_map, bound_variables=frozenset({}))¶ Performs the following substitutions in the given formula:
Substitute each occurrence of each constant name or variable name that is a key of the given constants and variables instantiation map with the term mapped to this name by this map.
Substitute each nullary invocation of each relation name that is a key of the given relations instantiation map with the formula mapped to it by this map.
For each unary invocation of each relation name that is a key of the given relations instantiation map, first perform all substitutions to the argument of this invocation (according to the given constants and variables instantiation map), then substitute the result for each occurrence of the constant name
'_'
in the formula mapped to the relation name by this map, and then substitute the result for this unary invocation of the relation name.
Only names originating in the given formula are substituted (i.e., names originating in one of the above substitutions are not subjected to additional substitutions).
 Parameters
formula (
Formula
) – formula in which to perform the substitutions.constants_and_variables_instantiation_map (
Mapping
[str
,Term
]) – mapping from constant names and variable names in the given formula to terms to be substituted for them, where the roots of terms mapped to variable names are variable names.relations_instantiation_map (
Mapping
[str
,Formula
]) – mapping from nullary and unary relation names in the given formula to formulas to be substituted for them, where formulas to be substituted for unary relation names are parametrized by the constant name'_'
.bound_variables (
AbstractSet
[str
]) – variables to be treated as bound (see below).
 Return type
 Returns
The result of all substitutions.
 Raises
BoundVariableError – if one of the following occurs when substituting an invocation of a relation name: 1. A free occurrence of a variable name in the formula mapped to the relation name by the given relations instantiation map is in
bound_variables
or becomes bound by a quantification in the given formula after all variable names in the given formula have been substituted. 2. For a unary invocation: a variable name that is in the argument to that invocation after all substitutions have been applied to this argument, becomes bound by a quantification in the formula mapped to the relation name by the given relations instantiation map.
Examples
The following succeeds:
>>> Schema._instantiate_helper( ... Formula.parse('Ax[(Q(c)>R(x))]'), {'x': Term('w')}, ... {'Q': Formula.parse('y=_')}, {'x', 'z'}) Aw[(y=c>R(w))]
however the following fails since
'Q(c)'
is to be substituted with'y=c'
while'y'
is in the given bound variables:>>> Schema._instantiate_helper( ... Formula.parse('Ax[(Q(c)>R(x))]'), {}, ... {'Q': Formula.parse('y=_')}, {'x', 'y', 'z'}) Traceback (most recent call last): ... predicates.proofs.Schema.BoundVariableError: ('y', 'Q')
and the following fails since as
'Q(c)'
is to be substituted with'y=c'
,'y'
is to become bound by the quantification'Ay'
:>>> Schema._instantiate_helper( ... Formula.parse('Ax[(Q(c)>R(x))]'), {'x': Term('y')}, ... {'Q': Formula.parse('y=_')}) Traceback (most recent call last): ... predicates.proofs.Schema.BoundVariableError: ('y', 'Q')
The following succeeds:
>>> Schema._instantiate_helper( ... Formula.parse('Ax[(Q(c)>R(x))]'), ... {'c': Term.parse('plus(d,x)')}, ... {'Q': Formula.parse('Ey[y=_]')}) Ax[(Ey[y=plus(d,x)]>R(x))]
however the following fails since as
'_'
is to be substituted with'plus(d,y)'
in'Ey[y=_]'
, the'y'
in'plus(d,y)'
is to become bound by the quantification'Ey'
:>>> Schema._instantiate_helper( ... Formula.parse('Ax[(Q(c)>R(x))]'), ... {'c': Term.parse('plus(d,y)')}, ... {'Q': Formula.parse('Ey[y=_]')}) Traceback (most recent call last): ... predicates.proofs.Schema.BoundVariableError: ('y', 'Q')

instantiate
(instantiation_map)¶ Instantiates the current schema according to the given map from templates of the current schema to expressions.
 Parameters
instantiation_map (
Mapping
[str
,Union
[Term
,str
,Formula
]]) – mapping from templates of the current schema to expressions of the type for which they serve as placeholders. That is, constant names are mapped to terms, variable names are mapped to variable names (strings), and relation names are mapped to formulas where unary relations are mapped to formulas parametrized by the constant name'_'
. Return type
 Returns
The predicatelogic formula obtained by applying the substitutions specified by the given map to the formula of the current schema:
Each occurrence in the formula of the current schema of each template constant name specified in the given map is substituted with the term to which that template constant name is mapped.
Each occurrence in the formula of the current schema of each template variable name specified in the given map is substituted with the variable name to which that template variable name is mapped.
Each nullary invocation in the formula of the current schema of each template relation name specified in the given map is substituted with the formula to which that template relation name is mapped.
Each unary invocation in the formula of the current schema of each template relation name specified in the given map is substituted with the formula to which that template relation name is mapped, in which each occurrence of the constant name
'_'
is substituted with the instantiated argument of that invocation of the template relation name (that is, the term that results from instantiating the argument of that invocation by performing all the specified substitutions on it).
None
is returned if one of the keys of the given map is not a template of the current schema or if one of the following occurs when substituting an invocation of a template relation name:A free occurrence of a variable name in the formula substituted for the template relation name becomes bound by a quantification in the instantiated schema formula, except if the template relation name is unary and this free occurrence originates in the instantiated argument of the relation invocation.
For a unary invocation: a variable name in the instantiated argument of that invocation becomes bound by a quantification in the formula that is substituted for the invocation of the template relation name.
Examples
>>> s = Schema(Formula.parse('(Q(c1,c2)>(R(c1)>R(c2)))'), ... {'c1', 'c2', 'R'}) >>> s.instantiate({'c1': Term.parse('plus(x,1)'), ... 'R': Formula.parse('Q(_,y)')}) (Q(plus(x,1),c2)>(Q(plus(x,1),y)>Q(c2,y))) >>> s.instantiate({'c1': Term.parse('plus(x,1)'), ... 'c2': Term.parse('c1'), ... 'R': Formula.parse('Q(_,y)')}) (Q(plus(x,1),c1)>(Q(plus(x,1),y)>Q(c1,y)))
>>> s = Schema(Formula.parse('(P()>P())'), {'P'}) >>> s.instantiate({'P': Formula.parse('plus(a,b)=c')}) (plus(a,b)=c>plus(a,b)=c)
For the following schema:
>>> s = Schema(Formula.parse('(Q(d)>Ax[(R(x)>Q(f(c)))])'), ... {'R', 'Q', 'x', 'c'})
the following succeeds:
>>> s.instantiate({'R': Formula.parse('_=0'), ... 'Q': Formula.parse('x=_'), ... 'x': 'w'}) (x=d>Aw[(w=0>x=f(c))])
however, the following returns
None
because'd'
is not a template of the schema:>>> s.instantiate({'R': Formula.parse('_=0'), ... 'Q': Formula.parse('x=_'), ... 'x': 'w', ... 'd': Term('z')})
and the following returns
None
because'z'
that is free in the assignment to'Q'
is to become bound by a quantification in the instantiated schema formula:>>> s.instantiate({'R': Formula.parse('_=0'), ... 'Q': Formula.parse('s(z)=_'), ... 'x': 'z'})
and the following returns
None
because'y'
in the instantiated argument'f(plus(a,y))'
of the second invocation of'Q'
is to become bound by the quantification in the formula substituted for'Q'
:>>> s.instantiate({'R': Formula.parse('_=0'), ... 'Q': Formula.parse('Ay[s(y)=_]'), ... 'c': Term.parse('plus(a,y)')})

class
predicates.proofs.
Proof
(assumptions, conclusion, lines)¶ Bases:
object
An immutable deductive proof in Predicate Logic, comprised of a list of assumptions/axioms, a conclusion, and a list of lines that prove the conclusion from (instances of) these assumptions/axioms and from tautologies, via the Modus Ponens (MP) and Universal Generalization (UG) inference rules.
 Variables

__init__
(assumptions, conclusion, lines)¶ Initializes a
Proof
from its assumptions/axioms, conclusion, and lines. Parameters
assumptions (
AbstractSet
[Schema
]) – the assumption/axioms for the proof.conclusion (
Formula
) – the conclusion for the proof.lines (
Sequence
[Union
[AssumptionLine
,MPLine
,UGLine
,TautologyLine
]]) – the lines for the proof.

class
AssumptionLine
(formula, assumption, instantiation_map)¶ Bases:
object
An immutable proof line justified as an instance of an assumption/axiom.
 Variables

__init__
(formula, assumption, instantiation_map)¶ Initializes an
AssumptionLine
from its formula, its justifying assumption, and its instantiation map from the justifying assumption.

__repr__
()¶ Computes a string representation of the current line.
 Return type
 Returns
A string representation of the current line.

is_valid
(assumptions, lines, line_number)¶ Checks if the current line is validly justified in the context of the specified proof.
 Parameters
assumptions (
AbstractSet
[Schema
]) – assumptions/axioms of the proof.lines (
Sequence
[Union
[AssumptionLine
,MPLine
,UGLine
,TautologyLine
]]) – lines of the proof.line_number (
int
) – line number of the current line in the given lines.
 Return type
 Returns
True
if the assumption/axiom of the current line is an assumption/axiom of the specified proof and if the formula justified by the current line is a valid instance of this assumption/axiom via the instantiation map of the current line,False
otherwise.

class
MPLine
(formula, antecedent_line_number, conditional_line_number)¶ Bases:
object
An immutable proof line justified by the Modus Ponens (MP) inference rule.
 Variables

__init__
(formula, antecedent_line_number, conditional_line_number)¶ Initializes a
MPLine
from its formula and line numbers of the antecedent and conditional of the MP inference justifying it.

__repr__
()¶ Computes a string representation of the current line.
 Return type
 Returns
A string representation of the current line.

is_valid
(assumptions, lines, line_number)¶ Checks if the current line is validly justified in the context of the specified proof.
 Parameters
assumptions (
AbstractSet
[Schema
]) – assumptions/axioms of the proof.lines (
Sequence
[Union
[AssumptionLine
,MPLine
,UGLine
,TautologyLine
]]) – lines of the proof.line_number (
int
) – line number of the current line in the given lines.
 Return type
 Returns
True
if the formula of the line from the given lines whose number is the conditional line number justifying the current line is'(
antecedent
>
consequent
)'
, whereantecedent
is the formula of the line from the given lines whose number is the antecedent line number justifying the current line andconsequent
is the formula justified by the current line;False
otherwise.

class
UGLine
(formula, predicate_line_number)¶ Bases:
object
An immutable proof line justified by the Universal Generalization (UG) inference rule.
 Variables

__init__
(formula, predicate_line_number)¶ Initializes a
UGLine
from its formula and line number of the predicate of the UG inference justifying it.

__repr__
()¶ Computes a string representation of the current line.
 Return type
 Returns
A string representation of the current line.

is_valid
(assumptions, lines, line_number)¶ Checks if the current line is validly justified in the context of the specified proof.
 Parameters
assumptions (
AbstractSet
[Schema
]) – assumptions/axioms of the proof.lines (
Sequence
[Union
[AssumptionLine
,MPLine
,UGLine
,TautologyLine
]]) – lines of the proof.line_number (
int
) – line number of the current line in the given lines.
 Return type
 Returns
True
if the formula of the current line is of the form'A
x
[
predicate
]'
, wherepredicate
is the formula of the line from the given lines whose number is the predicate line number justifying the current line andx
is any variable name;False
otherwise.

class
TautologyLine
(formula)¶ Bases:
object
An immutable proof line justified as a tautology.
 Variables
formula (
Formula
) – the formula justified by the line.

__init__
(formula)¶ Initializes a
TautologyLine
from its formula. Parameters
formula (
Formula
) – the formula to be justified by the line.

__repr__
()¶ Computes a string representation of the current line.
 Return type
 Returns
A string representation of the current line.

is_valid
(assumptions, lines, line_number)¶ Checks if the current line is validly justified in the context of the specified proof.
 Parameters
assumptions (
AbstractSet
[Schema
]) – assumptions/axioms of the proof.lines (
Sequence
[Union
[AssumptionLine
,MPLine
,UGLine
,TautologyLine
]]) – lines of the proof.line_number (
int
) – line number of the current line in the given lines.
 Return type
 Returns
True
if the formula justified by the current line is a (predicatelogic) tautology,False
otherwise.

Line
¶ An immutable proof line.

__repr__
()¶ Computes a string representation of the current proof.
 Return type
 Returns
A string representation of the current proof.

predicates.proofs.
I0_SCHEMA
¶ Schema equivalent of the propositionallogic self implication axiom
I0
.

predicates.proofs.
I1_SCHEMA
¶ Schema equivalent of the propositionallogic implication introduction (right) axiom
I1
.

predicates.proofs.
D_SCHEMA
¶ Schema equivalent of the propositionallogic selfdistribution of implication axiom
D
.

predicates.proofs.
I2_SCHEMA
¶ Schema equivalent of the propositionallogic implication introduction (left) axiom
I2
.

predicates.proofs.
N_SCHEMA
¶ Schema equivalent of the propositionallogic converse contraposition axiom
N
.

predicates.proofs.
NI_SCHEMA
¶ Schema equivalent of the propositionallogic negativeimplication introduction axiom
NI
.

predicates.proofs.
NN_SCHEMA
¶ Schema equivalent of the propositionallogic doublenegation introduction axiom
NN
.

predicates.proofs.
PROPOSITIONAL_AXIOMATIC_SYSTEM_SCHEMAS
¶ Schema system equivalent of the axioms of the propositionallogic large axiomatic system for implication and negation
AXIOMATIC_SYSTEM
.

predicates.proofs.
PROPOSITIONAL_AXIOM_TO_SCHEMA
¶ Mapping from propositionallogic axioms for implication and negation to their schema equivalents.

predicates.proofs.
_axiom_specialization_map_to_schema_instantiation_map
(propositional_specialization_map, substitution_map)¶ Converts the given propositionallogic specialization map from a propositionallogic axiom to its specialization, to an instantiation map from the schema equivalent of that axiom to a predicatelogic formula whose skeleton is that specialization.
 Parameters
propositional_specialization_map (
Mapping
[str
,Formula
]) – mapping specifying how some propositionallogic axiomaxiom
(which is not specified) fromAXIOMATIC_SYSTEM
specializes into some specializationspecialization
(which is also not specified), and containing no constants or operators beyond'~'
,'>'
,''
, and'&'
.substitution_map (
Mapping
[str
,Formula
]) – mapping from each atomic propositional subformula ofspecialization
to a predicatelogic formula.
 Return type
 Returns
An instantiation map for instantiating the schema equivalent of
axiom
into the predicatelogic formula obtained from its propositional skeletonspecialization
by the given substitution map.
Examples
>>> _axiom_specialization_map_to_schema_instantiation_map( ... {'p': PropositionalFormula.parse('(z1>z2)'), ... 'q': PropositionalFormula.parse('~z1')}, ... {'z1': Formula.parse('Ax[(x=5&M())]'), ... 'z2': Formula.parse('R(f(8,9))')}) {'P': (Ax[(x=5&M())]>R(f(8,9))), 'Q': ~Ax[(x=5&M())]}

predicates.proofs.
_prove_from_skeleton_proof
(formula, skeleton_proof, substitution_map)¶ Converts the given proof of a propositional skeleton of the given predicatelogic formula to a proof of that predicatelogic formula.
 Parameters
formula (
Formula
) – predicatelogic formula to prove.skeleton_proof (
Proof
) – valid propositionallogic proof of a propositional skeleton of the given formula, from no assumptions and viaAXIOMATIC_SYSTEM
, and containing no constants or operators beyond'~'
,'>'
,''
, and'&'
.substitution_map (
Mapping
[str
,Formula
]) – mapping from each atomic propositional subformula of the skeleton of the given formula that is proven in the given proof to the respective predicatelogic subformula of the given formula.
 Return type
 Returns
A valid predicatelogic proof of the given formula from the axioms
PROPOSITIONAL_AXIOMATIC_SYSTEM_SCHEMAS
via only assumption lines and MP lines.

predicates.proofs.
prove_tautology
(tautology)¶ Proves the given predicatelogic tautology.
 Parameters
tautology (
Formula
) – predicatelogic tautology to prove. Return type
 Returns
A valid proof of the given predicatelogic tautology from the axioms
PROPOSITIONAL_AXIOMATIC_SYSTEM_SCHEMAS
via only assumption lines and MP lines.