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Exactly one payment option: cash, card or voucher

Exactly one of cash, card or voucher, written as three mutually exclusive terms. Eight rows with three valid ones, a four-clause CNF that reads as the policy, and a Karnaugh map with three isolated cells.

A checkout accepts exactly one payment method, and the rule spells out the three allowed combinations: cash alone, card alone, or voucher alone, each term naming all three flags. The engine's reading lists those three cases. On the eight-row table over cash, card and voucher the output is true on three rows, Σm(1, 2, 4), and false on the five others, including the row with no method chosen and every row with two or three.

The checks: not a tautology, counterexample all three inputs FALSE; satisfiable, witness cash = FALSE, card = FALSE, voucher = TRUE. The simplifier found no law that shortens the fourteen-operator expression; the DNF is the original three terms. The CNF converter finds the shorter statement of the policy: (cash OR card OR voucher) AND (NOT cash OR NOT card) AND (NOT cash OR NOT voucher) AND (NOT card OR NOT voucher), four clauses and nine literals, which reads as “at least one, and no two together”. The Karnaugh map draws three single-cell groups, three prime implicants. Gate counts: 40 NAND, 67 NOR.

This is the exactly-one page with business names, and the CNF is the form worth keeping: the first clause is the “choose a method” validation, and the three pair clauses are the “only one method” validations, each a separate error message in a form. The thing to watch is the empty selection, which the rule rejects on row 0; a system that defaults to no method and skips validation when nothing was touched admits that row by accident. The at-most-one page shows what the rule looks like when the empty case is allowed.

valid := (cash AND NOT card AND NOT voucher) OR (NOT cash AND card AND NOT voucher) OR (NOT cash AND NOT card AND voucher) · output

Exact checks

Always true (tautology)? No Counterexample: cash = F, card = F, voucher = F · Exhaustively checked and solver cross-checked · 1 rows
Always false (contradiction)? No Counterexample: cash = F, card = F, voucher = T · Exhaustively checked and solver cross-checked · 2 rows
Can be true? Yes Example assignment: cash = F, card = F, voucher = T · Exhaustively checked and solver cross-checked · 2 rows

Truth table (8 rows)

Exactly one payment option: cash, card or voucher
#cashcardvouchervalid
0FALSEFALSEFALSEFALSE
1FALSEFALSETRUETRUE
2FALSETRUEFALSETRUE
3FALSETRUETRUEFALSE
4TRUEFALSEFALSETRUE
5TRUEFALSETRUEFALSE
6TRUETRUEFALSEFALSE
7TRUETRUETRUEFALSE

Plain-language reading

Beginnervalid is true exactly when at least one of the following holds (several may hold):
1. cash is true, card is false, and voucher is false
2. cash is false, card is true, and voucher is false
3. cash is false, card is false, and voucher is true
In every other case, valid is false.
About the operators:
- OR is inclusive: it is true when at least one part is true, including when several are.
- AND is true only when all of its parts are true.
- NOT reverses a value: true becomes false and false becomes true.
Intermediatevalid is true exactly when at least one of the following holds (several may hold):
1. cash is true, card is false, and voucher is false
2. cash is false, card is true, and voucher is false
3. cash is false, card is false, and voucher is true
In every other case, valid is false.
Advancedvalid is true exactly when at least one of the following holds (several may hold) [inclusive disjunction ∨]:
1. cash is true, card is false, and voucher is false [conjunction ∧]
2. cash is false, card is true, and voucher is false [conjunction ∧]
3. cash is false, card is false, and voucher is true [conjunction ∧]
In every other case, valid is false.
Formal notation: (cash ∧ ¬card ∧ ¬voucher) ∨ (¬cash ∧ card ∧ ¬voucher) ∨ (¬cash ∧ ¬card ∧ voucher)

Logic diagram

Exactly one payment option: cash, card or voucher Exactly one payment option: cash, card or voucher cash card voucher valid OR AND NOT NOT AND NOT NOT AND NOT NOT
Exactly one payment option: cash, card or voucher Exactly one payment option: cash, card or voucher cash card voucher valid OR AND NOT NOT AND NOT NOT AND NOT NOT

Simplification, step by step

The engine found no law that shortens this expression; it is already as short as its rewriting laws can make it.

(cash AND NOT card AND NOT voucher) OR (NOT cash AND card AND NOT voucher) OR (NOT cash AND NOT card AND voucher)

Karnaugh map

cash \ cardvoucher
00
01
11
10
0
0m0
1m1
0m3
1m2
1
1m4
0m5
0m7
0m6
  1. cells m1NOT cash AND NOT card AND voucher
  2. cells m2NOT cash AND card AND NOT voucher
  3. cells m4cash AND NOT card AND NOT voucher
(NOT cash AND NOT card AND voucher) OR (NOT cash AND card AND NOT voucher) OR (cash AND NOT card AND NOT voucher) · Derived (NOT cash AND NOT card AND voucher) OR (NOT cash AND card AND NOT voucher) OR (cash AND NOT card AND NOT voucher). Exactly equivalent on every assignment.

Minterms and maxterms

valid(cash, card, voucher) = Σm(1, 2, 4)valid(cash, card, voucher) = ΠM(0, 3, 5, 6, 7)

Variable order: cash, card, voucher · 8 rows

Normal forms

Conjunctive normal form (CNF)

(cash OR card OR voucher) AND (NOT cash OR NOT card) AND (NOT cash OR NOT voucher) AND (NOT card OR NOT voucher)

4 clauses, 9 literals · complete · Distribution ×2, Complement ×5, Absorption ×5, Idempotence ×1

Disjunctive normal form (DNF)

(cash AND NOT card AND NOT voucher) OR (NOT cash AND card AND NOT voucher) OR (NOT cash AND NOT card AND voucher)

3 terms, 9 literals · complete

NAND-only and NOR-only

NAND-only form

NAND(NAND(NAND(NAND(NAND(NAND(cash, NAND(card, card)), NAND(cash, NAND(card, card))), NAND(voucher, voucher)), NAND(NAND(NAND(NAND(cash, cash), card), NAND(NAND(cash, cash), card)), NAND(voucher, voucher))), NAND(NAND(NAND(NAND(cash, NAND(card, card)), NAND(cash, NAND(card, card))), NAND(voucher, voucher)), NAND(NAND(NAND(NAND(cash, cash), card), NAND(NAND(cash, cash), card)), NAND(voucher, voucher)))), NAND(NAND(NAND(NAND(cash, cash), NAND(card, card)), NAND(NAND(cash, cash), NAND(card, card))), voucher))

40 gates · verified equivalent on every row

NOR-only form

NOR(NOR(NOR(NOR(NOR(NOR(NOR(NOR(cash, cash), card), NOR(NOR(cash, cash), card)), voucher), NOR(NOR(NOR(cash, NOR(card, card)), NOR(cash, NOR(card, card))), voucher)), NOR(NOR(NOR(NOR(NOR(cash, cash), card), NOR(NOR(cash, cash), card)), voucher), NOR(NOR(NOR(cash, NOR(card, card)), NOR(cash, NOR(card, card))), voucher))), NOR(NOR(NOR(cash, card), NOR(cash, card)), NOR(voucher, voucher))), NOR(NOR(NOR(NOR(NOR(NOR(NOR(cash, cash), card), NOR(NOR(cash, cash), card)), voucher), NOR(NOR(NOR(cash, NOR(card, card)), NOR(cash, NOR(card, card))), voucher)), NOR(NOR(NOR(NOR(NOR(cash, cash), card), NOR(NOR(cash, cash), card)), voucher), NOR(NOR(NOR(cash, NOR(card, card)), NOR(cash, NOR(card, card))), voucher))), NOR(NOR(NOR(cash, card), NOR(cash, card)), NOR(voucher, voucher))))

67 gates · verified equivalent on every row

The same rule as code

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: 61dd28d6d3ab263c9e6d0b1c2132982144928c55e7d93bac9d3a8f60db77c999
Assumptions digest: d58ee1ad38e23e5093e4baa1047b5ae70d6972e08f555e34ac3fa16df63c4a78

Inputs (dict keys, declared order) and generated parameter names:
    'cash' -> input_cash
    'card' -> input_card
    'voucher' -> input_voucher

Outputs (declared order) and their functions:
    'valid' -> output_valid(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({'cash': False, 'card': False, 'voucher': False})
    # -> {'valid': False}
    model.output_valid({'cash': False, 'card': False, 'voucher': False})
    # -> False
    model.evaluate({'cash': 1, 'card': False, 'voucher': False})
    # 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_valid",
]

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": "61dd28d6d3ab263c9e6d0b1c2132982144928c55e7d93bac9d3a8f60db77c999",
    "assumptions_digest": "d58ee1ad38e23e5093e4baa1047b5ae70d6972e08f555e34ac3fa16df63c4a78",
    "primary_output": "valid",
    "unused_inputs": (),
    "subcircuits": (),
}

# Stable ID -> generated identifier (reversible mapping; names are exact, escaped strings).
IDENTIFIER_MAP = {
    "v_be76c451838e": {"kind": "input", "name": "cash", "identifier": "input_cash"},
    "v_c974ea178eba": {"kind": "input", "name": "card", "identifier": "input_card"},
    "v_c205843e647b": {"kind": "input", "name": "voucher", "identifier": "input_voucher"},
    "f_453ca86cbb3c": {"kind": "output", "name": "valid", "identifier": "output_valid"},
}

INPUT_NAMES = ("cash", "card", "voucher")
OUTPUT_NAMES = ("valid",)
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_valid(input_cash: bool, input_card: bool, input_voucher: bool) -> bool:
    """Decision output 'valid': (cash AND NOT card AND NOT voucher) OR (NOT cash AND card AND NOT voucher) OR (NOT cash AND NOT card AND voucher)"""
    return (input_cash and (not input_card) and (not input_voucher)) or ((not input_cash) and input_card and (not input_voucher)) or ((not input_cash) and (not input_card) and input_voucher)


# ---- Public API ----


def output_valid(inputs: Mapping[str, bool], *, check_scope: bool = True) -> bool:
    """Decision output 'valid' (stable ID f_453ca86cbb3c).

    'valid' := (cash AND NOT card AND NOT voucher) OR (NOT cash AND card AND NOT voucher) OR (NOT cash AND NOT card AND voucher)

    Required inputs: 'cash', 'card', 'voucher'.
    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, ("cash", "card", "voucher"), check_scope)
    if check_scope:
        _require_in_scope(values)
    output_valid_value = _compute_output_valid(values["cash"], values["card"], values["voucher"])
    return output_valid_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: 'cash', 'card', 'voucher'.
    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, ("cash", "card", "voucher"), check_scope)
    if check_scope:
        _require_in_scope(values)
    output_valid_value = _compute_output_valid(values["cash"], values["card"], values["voucher"])
    return {
        "valid": output_valid_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: 61dd28d6d3ab263c9e6d0b1c2132982144928c55e7d93bac9d3a8f60db77c999
-- 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_be76c451838e: cash -> "in_cash"
--   v_c974ea178eba: card -> "in_card"
--   v_c205843e647b: voucher -> "in_voucher"
-- Output columns:
--   f_453ca86cbb3c: valid -> "out_valid"
-- 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_valid] output valid (stable ID f_453ca86cbb3c)
--   valid := (cash AND NOT card AND NOT voucher) OR (NOT cash AND card AND NOT voucher) OR (NOT cash AND NOT card AND voucher)
--   PRECONDITION: "in_cash", "in_card", "in_voucher" are non-NULL booleans.
--   (("in_cash" AND (NOT "in_card") AND (NOT "in_voucher")) OR ((NOT "in_cash") AND "in_card" AND (NOT "in_voucher")) OR ((NOT "in_cash") AND (NOT "in_card") AND "in_voucher"))
--

-- ----------------------------------------------------------------------------------------------
-- 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_cash", "in_card", "in_voucher") AS (
  -- tangibool:example-rows:begin
  VALUES
    (1, FALSE, FALSE, FALSE),
    (2, FALSE, FALSE, TRUE),
    (3, FALSE, TRUE, FALSE),
    (4, FALSE, TRUE, TRUE),
    (5, TRUE, FALSE, FALSE),
    (6, TRUE, FALSE, TRUE),
    (7, TRUE, TRUE, FALSE),
    (8, TRUE, TRUE, TRUE),
    (9, NULL::boolean, FALSE, FALSE)
  -- tangibool:example-rows:end
),
checked AS (
  SELECT
    inputs.*,
    CASE
      WHEN "in_cash" IS NULL OR "in_card" IS NULL OR "in_voucher" IS NULL THEN 'invalid_input'
      ELSE 'ok'
    END AS "status"
  FROM inputs
)
SELECT
  "row_id",
  "in_cash",
  "in_card",
  "in_voucher",
  "status",
  CASE WHEN "status" = 'ok' THEN (("in_cash" AND (NOT "in_card") AND (NOT "in_voucher")) OR ((NOT "in_cash") AND "in_card" AND (NOT "in_voucher")) OR ((NOT "in_cash") AND (NOT "in_card") AND "in_voucher")) END AS "out_valid"
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: 61dd28d6d3ab263c9e6d0b1c2132982144928c55e7d93bac9d3a8f60db77c999
; 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_be76c451838e: cash -> in_cash
;   v_c974ea178eba: card -> in_card
;   v_c205843e647b: voucher -> in_voucher
;   f_453ca86cbb3c: valid -> out_valid

(set-option :produce-models true)
(set-info :smt-lib-version 2.6)
(set-logic QF_UF)

; ---- Inputs (declared order)
(declare-const in_cash Bool) ; cash
(declare-const in_card Bool) ; card
(declare-const in_voucher Bool) ; voucher

; ---- Outputs (dependencies first)
; output valid (stable ID f_453ca86cbb3c): (cash AND NOT card AND NOT voucher) OR (NOT cash AND card AND NOT voucher) OR (NOT cash AND NOT card AND voucher)
(define-fun out_valid () Bool (or (and in_cash (not in_card) (not in_voucher)) (and (not in_cash) in_card (not in_voucher)) (and (not in_cash) (not in_card) in_voucher)))

; ---- 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
valid = \left(\mathit{cash} \cdot \overline{\mathit{card}} \cdot \overline{\mathit{voucher}}\right) + \left(\overline{\mathit{cash}} \cdot \mathit{card} \cdot \overline{\mathit{voucher}}\right) + \left(\overline{\mathit{cash}} \cdot \overline{\mathit{card}} \cdot \mathit{voucher}\right)

The common slip

Writing the rule as cash XOR card XOR voucher. It agrees on seven rows and differs on cash = TRUE, card = TRUE, voucher = TRUE, where the XOR chain is true and the policy says no. A checkout that lets a customer tick all three would charge or credit in an unspecified way; the exactly-one page shows that row.

Questions

Why does the CNF have fewer operators but the same number of literals?

The three DNF terms each repeat all three flags, nine literals; the CNF spends its nine literals on one three-literal clause and three two-literal clauses. The converter counts both forms, and the table confirms them equal on all eight rows. Which is shorter depends on what you count.

Related

Operators and gates

Tools

See also

Worked examples

Generated from the Tangibool engine, semantics tangibool-semantics/1, engine 1.0.0, build . Every table, map, simplification and verdict on these pages was computed by the Tangibool engine when the site was built, and every claim was re-checked by the same exact checker the app uses. Limits are stated where they apply. © 2026 Foreranger LTD.