Una contradicción: A AND NOT A
A AND NOT A es falso en las dos filas de su tabla. La comprobación de contradicción se cumple, la satisfacibilidad se viola, y el simplificador reduce la fórmula a FALSE por la ley del complemento.
Una contradicción es una fórmula falsa en todas las filas: ninguna elección de entradas puede hacerla verdadera. A AND NOT A pide A y su negación a la vez, cosa que nunca ocurre. La lectura del motor es deliberadamente literal, never es verdadero exactamente cuando A es verdadero y A es falso, y la tabla de dos filas muestra la columna falsa en ambas: la lista de mintérminos está vacía y la lista de maxtérminos es ΠM(0, 1).
La contradicción se cumple: never es falso en todas las asignaciones. La satisfacibilidad se viola, la fórmula nunca puede ser verdadera, y la tautología se viola con el contraejemplo A = FALSO. El simplificador aplica la ley del complemento, registrada como A AND NOT A = FALSE, y lleva dos operadores a la constante FALSE en un paso. El conversor a FNC devuelve FALSE como una cláusula vacía y el de FND como disyunción vacía, cero términos. El mapa no dibuja grupos y deriva FALSE, cero implicantes primos. Compuertas: 5 NAND y 2 NOR, NOR(NOR(A, A), A).
Las contradicciones son lo que quieres de la negación de una propiedad de seguridad: si «los dos verdes encendidos» es una contradicción, el semáforo es seguro, que es lo que comprueba la página del semáforo. Son lo que no quieres de un conjunto de reglas: una política de acceso cuyas condiciones se contradicen no admite a nadie, y una configuración con restricciones contradictorias no tiene ningún estado válido. Lo que hay que vigilar es que una regla insatisfacible rara vez se parece a A AND NOT A; suele estar repartida entre varias cláusulas, y la comprobación de satisfacibilidad es como se encuentra.
never := A AND NOT A · salida
Comprobaciones exactas
Tabla de verdad (2 filas)
| # | A | never |
|---|---|---|
| 0 | FALSO | FALSO |
| 1 | VERDADERO | FALSO |
Lectura en lenguaje claro
Principiantenever es verdadero exactamente cuando A es verdadero y A es falso.
En todos los demás casos, never es falso.
Sobre los operadores:
- AND (Y) solo es verdadero cuando todas sus partes son verdaderas.
- NOT (NO) invierte un valor: lo verdadero pasa a ser falso y lo falso, verdadero.
Intermedionever es verdadero exactamente cuando A es verdadero y A es falso.
En todos los demás casos, never es falso.
Avanzadonever es verdadero exactamente cuando A es verdadero y A es falso [conjunción ∧].
En todos los demás casos, never es falso.
Notación formal: A ∧ ¬A
Diagrama lógico
Simplificación paso a paso
A AND NOT A- Complemento ·
A AND NOT A = FALSEA AND NOT A→FALSEResultado:FALSE
Mapa de Karnaugh
Mintérminos y maxtérminos
never(A) = Σm()never(A) = ΠM(0, 1)Orden de variables: A · 2 filas
Formas normales
Forma normal conjuntiva (FNC)
FALSE1 cláusulas, 0 literales · complete · Complemento ×1
Forma normal disyuntiva (FND)
FALSE0 términos, 0 literales · complete · Complemento ×1
Solo NAND, solo NOR
Forma solo con NAND
NAND(NAND(A, NAND(A, A)), NAND(A, NAND(A, A)))5 compuertas · equivalencia verificada en todas las filas
Forma solo con NOR
NOR(NOR(A, A), A)2 compuertas · equivalencia verificada en todas las filas
La misma regla como código
Python
# -*- coding: utf-8 -*-
# Generated by Tangibool (tangibool.python/1). Do not edit by hand; regenerate from the source revision.
# Model: not stated
# Source revision: reference
# Interpretation status: not stated
"""Tangibool evaluator (decision model).
Generated deterministically from the validated Boolean model; it evaluates exactly that
model. It does not establish that the model is a complete, legal, or safe statement of a
real-world rule, and evaluating examples does not verify the rule.
Source revision: reference
Interpretation status: not stated
Exporter: 1.0.0 (format tangibool.python/1; engine 1.0.0; semantics tangibool-semantics/1)
Logic digest: 5542a051af1189095323c8274f7cba4b2a268d065449331a44bf652258eb6294
Assumptions digest: d58ee1ad38e23e5093e4baa1047b5ae70d6972e08f555e34ac3fa16df63c4a78
Inputs (dict keys, declared order) and generated parameter names:
'A' -> input_A
Outputs (declared order) and their functions:
'never' -> output_never(inputs)
Assumptions (the declared scope, checked by in_scope(inputs)):
none; every complete assignment is in scope.
Input contract:
Every required input must be exactly True or False (type(value) is bool). Missing
inputs, None, strings, integers (including 0 and 1), and keys that are not declared
inputs raise InputError before anything is evaluated, including inputs that a
short-circuiting operator would never read. Results are always bool.
Scope:
Decision functions raise OutOfScopeError when the inputs violate an assumption; an
out-of-scope assignment is never turned into a False result. Pass check_scope=False
to evaluate without the scope check, and use in_scope(inputs) to test it separately.
Usage:
import tangibool_model as model
model.evaluate({'A': False})
# -> {'never': False}
model.output_never({'A': False})
# -> False
model.evaluate({'A': 1})
# raises InputError: 1 is an int, not a bool
"""
import collections.abc as _abc
from typing import Dict, Mapping, Tuple
__all__ = [
"MODEL_INFO",
"IDENTIFIER_MAP",
"INPUT_NAMES",
"OUTPUT_NAMES",
"ASSUMPTIONS",
"InputError",
"OutOfScopeError",
"minterm_index",
"in_scope",
"evaluate",
"output_never",
]
MODEL_INFO = {
"format": "tangibool.python/1",
"mode": "decision",
"model": None,
"revision": "reference",
"interpretation": None,
"exporter": "1.0.0",
"engine_version": "1.0.0",
"semantics_version": "tangibool-semantics/1",
"logic_digest": "5542a051af1189095323c8274f7cba4b2a268d065449331a44bf652258eb6294",
"assumptions_digest": "d58ee1ad38e23e5093e4baa1047b5ae70d6972e08f555e34ac3fa16df63c4a78",
"primary_output": "never",
"unused_inputs": (),
"subcircuits": (),
}
# Stable ID -> generated identifier (reversible mapping; names are exact, escaped strings).
IDENTIFIER_MAP = {
"v_c164641b9b32": {"kind": "input", "name": "A", "identifier": "input_A"},
"f_07e2a0a6c537": {"kind": "output", "name": "never", "identifier": "output_never"},
}
INPUT_NAMES = ("A",)
OUTPUT_NAMES = ("never",)
ASSUMPTIONS = ()
_DECLARED_INPUTS = frozenset(INPUT_NAMES)
_SCOPE_INPUTS = ()
_ASSUMPTION_FORMULAS = {entry["name"]: entry["formula"] for entry in ASSUMPTIONS}
class InputError(ValueError):
"""Raised when inputs are missing, undeclared, or not exactly True/False.
Every required input must satisfy type(value) is bool. Missing inputs, None, strings,
integers (including 0 and 1), and keys that are not declared inputs are rejected before
anything is evaluated. A missing input is never treated as False. The individual problems
are listed in the problems attribute.
"""
def __init__(self, problems):
self.problems = tuple(problems)
super().__init__("Invalid inputs: " + "; ".join(self.problems))
class OutOfScopeError(ValueError):
"""Raised when the inputs violate the model's assumptions (its declared scope).
Outside its assumptions the rule has no decision: this error is never a False result.
The names of the violated assumptions are in the violated attribute.
"""
def __init__(self, violated):
self.violated = tuple(violated)
details = ", ".join(name + " (" + _ASSUMPTION_FORMULAS.get(name, "?") + ")" for name in self.violated)
super().__init__(
"Out of scope: the inputs violate "
+ ("assumption " if len(self.violated) == 1 else "assumptions ")
+ details
+ ". The rule has no decision outside its assumptions; this is not a False result."
)
def _short_repr(value: object) -> str:
text = repr(value)
return text if len(text) <= 60 else text[:57] + "..."
def _checked_inputs(inputs: Mapping[str, bool], required: Tuple[str, ...], check_scope: bool) -> Dict[str, bool]:
"""Validate inputs strictly before anything is evaluated and return a plain copy."""
if type(check_scope) is not bool:
raise TypeError("check_scope must be True or False")
if not isinstance(inputs, _abc.Mapping):
raise InputError(["inputs must be a mapping from input names to True/False, got " + type(inputs).__name__])
problems = []
for key in inputs:
if type(key) is not str or key not in _DECLARED_INPUTS:
declared = ", ".join(repr(name) for name in INPUT_NAMES) or "none"
problems.append("undeclared input " + _short_repr(key) + " (declared inputs: " + declared + ")")
needed = tuple(required) + (_SCOPE_INPUTS if check_scope else ())
for name in needed:
if name not in inputs:
problems.append("missing required input " + repr(name))
for key, value in inputs.items():
if type(key) is str and key in _DECLARED_INPUTS and type(value) is not bool:
problems.append(
"input " + repr(key) + " must be True or False (type bool), got "
+ type(value).__name__ + " " + _short_repr(value)
)
if problems:
raise InputError(list(dict.fromkeys(problems)))
return dict(inputs.items())
def _require_bool_args(function: str, pairs: Tuple[Tuple[str, object], ...]) -> None:
problems = [
"argument " + repr(name) + " of " + function + " must be True or False (type bool), got "
+ type(value).__name__ + " " + _short_repr(value)
for name, value in pairs
if type(value) is not bool
]
if problems:
raise InputError(problems)
def minterm_index(*values: bool) -> int:
"""Row index of an assignment over a declared variable order.
The first value is the most significant bit, so all-False is row 0. Used for indexed
minterm (sum) and maxterm (product) forms.
"""
index = 0
for value in values:
if type(value) is not bool:
raise InputError(["minterm_index() takes True/False values, got " + type(value).__name__ + " " + _short_repr(value)])
index = index * 2 + (1 if value else 0)
return index
def _scope_values(values: Dict[str, bool]) -> Tuple[Tuple[str, bool], ...]:
"""Value of every enabled, confirmed assumption for validated inputs, in declared order."""
return ()
def _require_in_scope(values: Dict[str, bool]) -> None:
violated = tuple(name for name, holds in _scope_values(values) if not holds)
if violated:
raise OutOfScopeError(violated)
def in_scope(inputs: Mapping[str, bool]) -> bool:
"""True when the inputs satisfy every assumption (the model's declared scope).
Requires the inputs the assumptions read; raises InputError for invalid inputs.
"""
values = _checked_inputs(inputs, (), True)
return all(holds for _, holds in _scope_values(values))
# ---- Formula bodies (inputs are validated by the public functions below) ----
def _compute_output_never(input_A: bool) -> bool:
"""Decision output 'never': A AND NOT A"""
return input_A and (not input_A)
# ---- Public API ----
def output_never(inputs: Mapping[str, bool], *, check_scope: bool = True) -> bool:
"""Decision output 'never' (stable ID f_07e2a0a6c537).
'never' := A AND NOT A
Required inputs: 'A'.
Raises InputError for missing, undeclared, or non-bool inputs, and OutOfScopeError
when check_scope is True and the inputs violate an assumption.
"""
values = _checked_inputs(inputs, ("A",), check_scope)
if check_scope:
_require_in_scope(values)
output_never_value = _compute_output_never(values["A"])
return output_never_value
def evaluate(inputs: Mapping[str, bool], *, check_scope: bool = True) -> Dict[str, bool]:
"""Evaluate every output (declared order); each output is computed once.
Required inputs: 'A'.
Raises InputError for missing, undeclared, or non-bool inputs, and OutOfScopeError
when check_scope is True and the inputs violate an assumption.
"""
values = _checked_inputs(inputs, ("A",), check_scope)
if check_scope:
_require_in_scope(values)
output_never_value = _compute_output_never(values["A"])
return {
"never": output_never_value,
}
PostgreSQL
-- Tangibool PostgreSQL export (tangibool.postgresql/1)
-- Target: PostgreSQL 16 or later with typed boolean inputs; tested with PostgreSQL 18.3 (PGlite 0.5.8).
-- Not a claim of compatibility with other SQL dialects.
-- Model: not stated
-- Source revision: reference
-- Interpretation status: not stated
-- Exporter: 1.0.0 (engine 1.0.0; semantics tangibool-semantics/1)
-- Logic digest: 5542a051af1189095323c8274f7cba4b2a268d065449331a44bf652258eb6294
-- Assumptions digest: d58ee1ad38e23e5093e4baa1047b5ae70d6972e08f555e34ac3fa16df63c4a78
-- Mode: decision
--
-- Read-only: this file contains only WITH / VALUES / SELECT statements. No DDL, DML,
-- procedures, credentials, network access, or database changes. The expressions are pure
-- Boolean expressions, so their result does not depend on SQL evaluation order.
--
-- NON-NULL INPUT PRECONDITION: NULL is not a truth value of this rule. Every fragment below
-- is defined only when every input column it reads is a non-NULL boolean. The guard template
-- (section 2) marks any NULL input as 'invalid_input' and any row that violates the
-- assumptions as 'out_of_scope', and fills output columns only for 'ok' rows; a NULL in an
-- output column of another row is an envelope marker, not a third truth value. Never wrap
-- the fragments in COALESCE(..., FALSE) or otherwise choose a meaning for unknown inputs.
-- This evaluates the supplied model; it does not show that the model is a complete, legal,
-- or safe statement of a real-world rule.
--
-- Input columns (stable ID: name -> column):
-- v_c164641b9b32: A -> "in_A"
-- Output columns:
-- f_07e2a0a6c537: never -> "out_never"
-- Assumptions (scope K; exported separately and never folded into an output):
-- none; every complete input row is in scope.
-- ----------------------------------------------------------------------------------------------
-- 1. Expression fragments (parenthesised; non-NULL boolean inputs required)
-- ----------------------------------------------------------------------------------------------
--
-- [out_never] output never (stable ID f_07e2a0a6c537)
-- never := A AND NOT A
-- PRECONDITION: "in_A" is a non-NULL boolean.
-- ("in_A" AND (NOT "in_A"))
--
-- ----------------------------------------------------------------------------------------------
-- 2. Guard template (read-only SELECT over an inputs list)
-- ----------------------------------------------------------------------------------------------
-- Replace the example rows between the markers with your own rows, or replace the inputs
-- CTE with a SELECT that provides the boolean columns listed in the header. status is
-- 'invalid_input' when any input is NULL, 'out_of_scope' when the assumptions are false, and
-- 'ok' otherwise; output columns are filled only for 'ok' rows (NULL elsewhere is an
-- envelope marker). Assumption columns are shown for rows with complete inputs.
WITH inputs ("row_id", "in_A") AS (
-- tangibool:example-rows:begin
VALUES
(1, FALSE),
(2, TRUE),
(3, NULL::boolean)
-- tangibool:example-rows:end
),
checked AS (
SELECT
inputs.*,
CASE
WHEN "in_A" IS NULL THEN 'invalid_input'
ELSE 'ok'
END AS "status"
FROM inputs
)
SELECT
"row_id",
"in_A",
"status",
CASE WHEN "status" = 'ok' THEN ("in_A" AND (NOT "in_A")) END AS "out_never"
FROM checked
ORDER BY "row_id";
SMT-LIB
; Tangibool SMT-LIB export (tangibool.smtlib/1) ; Profile: SMT-LIB 2.6 Boolean subset (QF_UF): Bool constants, define-fun, let, push/pop, assert, check-sat, echo. ; Tested with Z3 5.1.0 (z3-solver 5.2.0, WebAssembly build). ; Model: not stated ; Source revision: reference ; Interpretation status: not stated ; Exporter: 1.0.0 (engine 1.0.0; semantics tangibool-semantics/1) ; Logic digest: 5542a051af1189095323c8274f7cba4b2a268d065449331a44bf652258eb6294 ; Assumptions digest: d58ee1ad38e23e5093e4baa1047b5ae70d6972e08f555e34ac3fa16df63c4a78 ; Mode: decision ; ; Reading results: each query block states what sat and unsat mean for its question. A sat ; answer comes with a witness or counterexample (ask for it with (get-model) after sat only); ; unsat settles that scoped query and is solver-checked, not an independently checked proof ; certificate; unknown settles nothing. Blocks are scoped with push/pop, so assertions never ; accumulate across questions. This checks the supplied model, not whether it is a complete, ; legal, or safe statement of a real-world rule. ; ; Symbols (stable ID: name -> symbol): ; v_c164641b9b32: A -> in_A ; f_07e2a0a6c537: never -> out_never (set-option :produce-models true) (set-info :smt-lib-version 2.6) (set-logic QF_UF) ; ---- Inputs (declared order) (declare-const in_A Bool) ; A ; ---- Outputs (dependencies first) ; output never (stable ID f_07e2a0a6c537): A AND NOT A (define-fun out_never () Bool (and in_A (not in_A))) ; ---- Assumptions (the scope K; never folded into an output) ; K: conjunction of the enabled, confirmed assumptions (true when there are none) (define-fun K () Bool true) ; ---- Definitions only: nothing is asserted and no check is run. ; Add (assert ...) and (check-sat) inside (push 1) ... (pop 1) to ask a question.
LaTeX
never = A \cdot \overline{A}El error habitual
Tratar «insatisfacible» como un fallo del comprobador cuando la regla es larga. Una regla con cinco condiciones sin ninguna fila que la satisfaga te está diciendo que dos de sus condiciones se excluyen. El ejemplo de dos filas es ese fallo en miniatura: A AND NOT A, y la ley del complemento le pone nombre.
Preguntas
¿Por qué la FND tiene cero términos pero la FNC tiene uno?
FALSE como disyunción es la vacía, sin ningún término que la haga verdadera; FALSE como conjunción es una sola cláusula sin literales, que no puede satisfacerse. Los conversores informan de los recuentos de términos y literales que hacen que cada forma se lea como la constante, y la tabla confirma las dos.
Relacionado
Leyes
Operadores y compuertas
- Compuerta NOT (inversor): tabla de verdad, símbolo y el operador NOT
- Compuerta AND (puerta Y): tabla de verdad de 2, 3 y 4 entradas, símbolo y expresión
Herramientas
- Generador de tablas de verdad: cualquier expresión booleana, hasta 12 variables, con columnas intermedias
- Calculadora y simplificador de álgebra de Boole paso a paso (cada ley nombrada y verificada)
- Solucionador de mapas de Karnaugh: de 2 a 4 variables, agrupaciones, SOP y POS
Ejercicios
Véase también
- Contradicción: definición, ejemplo y equivalente en inglés
- Una tautología: A OR NOT A, comprobada en todas las filas
- Propiedad de seguridad de un semáforo: nunca dos verdes, comprobada como «siempre verdadera»
- Premisas inconsistentes: A y NOT A demuestran cualquier cosa (validez vacua)
- Ley del complemento: A·A' = 0, A+A' = 1
- Satisfacible: definición, ejemplo y equivalente en inglés
Ejemplos resueltos
Generado a partir del motor de Tangibool, semántica tangibool-semantics/1, motor 1.0.0, compilación . Cada tabla, mapa, simplificación y veredicto de estas páginas lo calculó el motor de Tangibool al compilar el sitio, y cada afirmación la volvió a comprobar el mismo verificador exacto que usa la app. Los límites se indican donde aplican. © 2026 Foreranger LTD.