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BCD digit greater than five: four-variable K-map with don’t-cares

Is a BCD digit greater than five? The function Σm(D, C, B, A; 6, 7, 8, 9) under the assumption that codes 10 to 15 never occur. Six don't-care cells let the Karnaugh map derive the two-term D OR (C AND B).

The inputs D, C, B, A are the 8, 4, 2 and 1 bits of a decimal digit, and the output is true for 6, 7, 8 and 9, which is the minterm list in the formula. The assumption k1, NOT (D AND (C OR B)), says the four bits always encode a digit 0 to 9, so the six codes from 10 to 15 are excluded; in the sixteen-row table the assumption column is false on exactly those six rows. The engine's reading restates the formula as the rows 6, 7, 8 and 9 of the table.

The tautology check is violated with the counterexample of all four inputs FALSE, and satisfiability holds with the witness D = FALSE, C = TRUE, B = TRUE, A = FALSE, the digit 6. The simplifier found no law to apply to a minterm list. The converter expands it into a four-term, sixteen-literal DNF and a twelve-clause, 48-literal CNF; the gate converters report 95 NAND and 191 NOR for that expansion. The Karnaugh map, with 6 don't-care cells from the assumption, draws two groups, D and C AND B, two prime implicants, and derives D OR (C AND B), labelled equivalent within the assumptions.

Threshold tests on encoded values are common in decoders, in range checks on enums and in validation code, and this one shows how much an honest assumption buys: a four-term expansion becomes two terms because the map may treat the impossible codes as whatever is convenient. The thing to watch is exactly that convenience. D OR (C AND B) is true on codes 10 to 15, so if such a code ever arrives the shortened test reports greater-than-five for inputs the original never specified. The assumption must be true in the system, not just stated in the model.

greater_than_five := Σm(D, C, B, A; 6, 7, 8, 9) · output

Assumptions: NOT (D AND (C OR B)) (The four bits encode a decimal digit 0 to 9 (BCD); codes 10 to 15 never occur.)

Exact checks

Always true (tautology)? No Counterexample: D = F, C = F, B = F, A = F · Exhaustively checked and solver cross-checked · 1 rows
Always false (contradiction)? No Counterexample: D = F, C = T, B = T, A = F · Exhaustively checked and solver cross-checked · 7 rows
Can be true? Yes Example assignment: D = F, C = T, B = T, A = F · Exhaustively checked and solver cross-checked · 7 rows
Are the assumptions consistent? Yes Example assignment: D = F, C = F, B = F, A = F · Exhaustively checked and solver cross-checked · 1 rows

Truth table (16 rows)

BCD digit greater than five: four-variable K-map with don’t-cares
#DCBAgreater_than_fivek1Scope
0FALSEFALSEFALSEFALSEFALSETRUEin scope
1FALSEFALSEFALSETRUEFALSETRUEin scope
2FALSEFALSETRUEFALSEFALSETRUEin scope
3FALSEFALSETRUETRUEFALSETRUEin scope
4FALSETRUEFALSEFALSEFALSETRUEin scope
5FALSETRUEFALSETRUEFALSETRUEin scope
6FALSETRUETRUEFALSETRUETRUEin scope
7FALSETRUETRUETRUETRUETRUEin scope
8TRUEFALSEFALSEFALSETRUETRUEin scope
9TRUEFALSEFALSETRUETRUETRUEin scope
10TRUEFALSETRUEFALSEFALSEFALSEexcluded
11TRUEFALSETRUETRUEFALSEFALSEexcluded
12TRUETRUEFALSEFALSEFALSEFALSEexcluded
13TRUETRUEFALSETRUEFALSEFALSEexcluded
14TRUETRUETRUEFALSEFALSEFALSEexcluded
15TRUETRUETRUETRUEFALSEFALSEexcluded

Plain-language reading

Beginnergreater_than_five is true exactly when the truth-table row of (D, C, B, A) is one of the rows 6, 7, 8, and 9.
In every other case, greater_than_five is false.
About the operators:
- Σm lists the truth-table rows (minterms) where the formula is true. Rows are numbered from 0 with the first listed input as the most significant bit.
Intermediategreater_than_five is true exactly when the truth-table row of (D, C, B, A) is one of the rows 6, 7, 8, and 9.
In every other case, greater_than_five is false.
Advancedgreater_than_five is true exactly when the truth-table row of (D, C, B, A) is one of the rows 6, 7, 8, and 9 [canonical sum of minterms (DNF)].
In every other case, greater_than_five is false.
Formal notation: Σm(D, C, B, A; 6, 7, 8, 9)

Logic diagram

BCD digit greater than five: four-variable K-map with don’t-cares BCD digit greater than five: four-variable K-map with don’t-cares D C B A greater_than_five k1ASSUME Σm(6,7,8,9)DCBA NOT AND OR
BCD digit greater than five: four-variable K-map with don’t-cares BCD digit greater than five: four-variable K-map with don’t-cares D C B A greater_than_five k1ASSUME Σm(6,7,8,9)DCBA NOT AND OR

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.

Σm(D, C, B, A; 6, 7, 8, 9)

Karnaugh map

DC \ BA
00
01
11
10
00
0m0
0m1
0m3
0m2
01
0m4
0m5
1m7
1m6
11
Xm12
Xm13
Xm15
Xm14
10
1m8
1m9
Xm11
Xm10
  1. cells m8, m9, m10, m11, m12, m13, m14, m15D
  2. cells m6, m7, m14, m15C AND B
D OR (C AND B) · Derived D OR (C AND B). The groups use don't-care cells, so the result is only claimed within the assumptions. Equivalent on every assignment the assumptions allow (scoped: it was derived using the assumptions); no claim is made outside them.

6 cells excluded by the confirmed assumptions (k1) are marked don't-care. An expression derived with them is equivalent only within the assumptions.

Minterms and maxterms

greater_than_five(D, C, B, A) = Σm(6, 7, 8, 9)greater_than_five(D, C, B, A) = ΠM(0, 1, 2, 3, 4, 5, 10, 11, 12, 13, 14, 15)

Variable order: D, C, B, A · 16 rows

Normal forms

Conjunctive normal form (CNF)

(D OR C OR B OR A) AND (D OR C OR B OR NOT A) AND (D OR C OR NOT B OR A) AND (D OR C OR NOT B OR NOT A) AND (D OR NOT C OR B OR A) AND (D OR NOT C OR B OR NOT A) AND (NOT D OR C OR NOT B OR A) AND (NOT D OR C OR NOT B OR NOT A) AND (NOT D OR NOT C OR B OR A) AND (NOT D OR NOT C OR B OR NOT A) AND (NOT D OR NOT C OR NOT B OR A) AND (NOT D OR NOT C OR NOT B OR NOT A)

12 clauses, 48 literals · complete · Minterm expansion ×1

Disjunctive normal form (DNF)

(D AND NOT C AND NOT B AND A) OR (D AND NOT C AND NOT B AND NOT A) OR (NOT D AND C AND B AND A) OR (NOT D AND C AND B AND NOT A)

4 terms, 16 literals · complete · Minterm expansion ×1

NAND-only and NOR-only

NAND-only form

NAND(NAND(NAND(NAND(NAND(NAND(NAND(D, D), C), NAND(NAND(D, D), C)), NAND(NAND(B, NAND(A, A)), NAND(B, NAND(A, A)))), NAND(NAND(NAND(NAND(D, D), C), NAND(NAND(D, D), C)), NAND(NAND(B, A), NAND(B, A)))), NAND(NAND(NAND(NAND(NAND(D, D), C), NAND(NAND(D, D), C)), NAND(NAND(B, NAND(A, A)), NAND(B, NAND(A, A)))), NAND(NAND(NAND(NAND(D, D), C), NAND(NAND(D, D), C)), NAND(NAND(B, A), NAND(B, A))))), NAND(NAND(NAND(NAND(NAND(D, NAND(C, C)), NAND(D, NAND(C, C))), NAND(NAND(NAND(B, B), NAND(A, A)), NAND(NAND(B, B), NAND(A, A)))), NAND(NAND(NAND(D, NAND(C, C)), NAND(D, NAND(C, C))), NAND(NAND(NAND(B, B), A), NAND(NAND(B, B), A)))), NAND(NAND(NAND(NAND(D, NAND(C, C)), NAND(D, NAND(C, C))), NAND(NAND(NAND(B, B), NAND(A, A)), NAND(NAND(B, B), NAND(A, A)))), NAND(NAND(NAND(D, NAND(C, C)), NAND(D, NAND(C, C))), NAND(NAND(NAND(B, B), A), NAND(NAND(B, B), A))))))

95 gates · verified equivalent on every row

NOR-only form

NOR(NOR(NOR(NOR(NOR(NOR(NOR(D, NOR(C, C)), NOR(D, NOR(C, C))), NOR(NOR(NOR(B, B), A), NOR(NOR(B, B), A))), NOR(NOR(NOR(D, NOR(C, C)), NOR(D, NOR(C, C))), NOR(NOR(NOR(B, B), NOR(A, A)), NOR(NOR(B, B), NOR(A, A))))), NOR(NOR(NOR(NOR(D, NOR(C, C)), NOR(D, NOR(C, C))), NOR(NOR(NOR(B, B), A), NOR(NOR(B, B), A))), NOR(NOR(NOR(D, NOR(C, C)), NOR(D, NOR(C, C))), NOR(NOR(NOR(B, B), NOR(A, A)), NOR(NOR(B, B), NOR(A, A)))))), NOR(NOR(NOR(NOR(NOR(NOR(D, D), C), NOR(NOR(D, D), C)), NOR(NOR(B, A), NOR(B, A))), NOR(NOR(NOR(NOR(D, D), C), NOR(NOR(D, D), C)), NOR(NOR(B, NOR(A, A)), NOR(B, NOR(A, A))))), NOR(NOR(NOR(NOR(NOR(D, D), C), NOR(NOR(D, D), C)), NOR(NOR(B, A), NOR(B, A))), NOR(NOR(NOR(NOR(D, D), C), NOR(NOR(D, D), C)), NOR(NOR(B, NOR(A, A)), NOR(B, NOR(A, A))))))), NOR(NOR(NOR(NOR(NOR(NOR(D, NOR(C, C)), NOR(D, NOR(C, C))), NOR(NOR(NOR(B, B), A), NOR(NOR(B, B), A))), NOR(NOR(NOR(D, NOR(C, C)), NOR(D, NOR(C, C))), NOR(NOR(NOR(B, B), NOR(A, A)), NOR(NOR(B, B), NOR(A, A))))), NOR(NOR(NOR(NOR(D, NOR(C, C)), NOR(D, NOR(C, C))), NOR(NOR(NOR(B, B), A), NOR(NOR(B, B), A))), NOR(NOR(NOR(D, NOR(C, C)), NOR(D, NOR(C, C))), NOR(NOR(NOR(B, B), NOR(A, A)), NOR(NOR(B, B), NOR(A, A)))))), NOR(NOR(NOR(NOR(NOR(NOR(D, D), C), NOR(NOR(D, D), C)), NOR(NOR(B, A), NOR(B, A))), NOR(NOR(NOR(NOR(D, D), C), NOR(NOR(D, D), C)), NOR(NOR(B, NOR(A, A)), NOR(B, NOR(A, A))))), NOR(NOR(NOR(NOR(NOR(D, D), C), NOR(NOR(D, D), C)), NOR(NOR(B, A), NOR(B, A))), NOR(NOR(NOR(NOR(D, D), C), NOR(NOR(D, D), C)), NOR(NOR(B, NOR(A, A)), NOR(B, NOR(A, A))))))))

191 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: 7eb00dd03ae1ec07d2792c847f4e5db34288ea51c001af5f2977ef79fd88dcb3
Assumptions digest: 25076d78f029a36624a87032d35dc97d625d1c5ab40292fcb6e7c5f036915ed7

Inputs (dict keys, declared order) and generated parameter names:
    'D' -> input_D
    'C' -> input_C
    'B' -> input_B
    'A' -> input_A

Outputs (declared order) and their functions:
    'greater_than_five' -> output_greater_than_five(inputs)

Assumptions (the declared scope, checked by in_scope(inputs)):
    'k1': NOT (D AND (C OR B))

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({'D': False, 'C': False, 'B': False, 'A': False})
    # -> {'greater_than_five': False}
    model.output_greater_than_five({'D': False, 'C': False, 'B': False, 'A': False})
    # -> False
    model.evaluate({'D': 1, 'C': False, 'B': False, 'A': 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_greater_than_five",
    "assumption_k1",
]

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": "7eb00dd03ae1ec07d2792c847f4e5db34288ea51c001af5f2977ef79fd88dcb3",
    "assumptions_digest": "25076d78f029a36624a87032d35dc97d625d1c5ab40292fcb6e7c5f036915ed7",
    "primary_output": "greater_than_five",
    "unused_inputs": (),
    "subcircuits": (),
}

# Stable ID -> generated identifier (reversible mapping; names are exact, escaped strings).
IDENTIFIER_MAP = {
    "v_095da454e794": {"kind": "input", "name": "D", "identifier": "input_D"},
    "v_18ad16a71134": {"kind": "input", "name": "C", "identifier": "input_C"},
    "v_7fc0ba5488b3": {"kind": "input", "name": "B", "identifier": "input_B"},
    "v_b93ff9520200": {"kind": "input", "name": "A", "identifier": "input_A"},
    "f_2d3893154eb6": {"kind": "output", "name": "greater_than_five", "identifier": "output_greater_than_five"},
    "f_180149c5249a": {"kind": "assumption", "name": "k1", "identifier": "assumption_k1"},
}

INPUT_NAMES = ("D", "C", "B", "A")
OUTPUT_NAMES = ("greater_than_five",)
ASSUMPTIONS = (
    {"name": "k1", "id": "f_180149c5249a", "formula": "NOT (D AND (C OR B))", "description": "The four bits encode a decimal digit 0 to 9 (BCD); codes 10 to 15 never occur."},
)

_DECLARED_INPUTS = frozenset(INPUT_NAMES)
_SCOPE_INPUTS = ("D", "C", "B")
_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."""
    assumption_k1_value = _compute_assumption_k1(values["D"], values["C"], values["B"])
    return (
        ("k1", assumption_k1_value),
    )


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_greater_than_five(input_D: bool, input_C: bool, input_B: bool, input_A: bool) -> bool:
    """Decision output 'greater_than_five': \u03a3m(D, C, B, A; 6, 7, 8, 9)"""
    return minterm_index(input_D, input_C, input_B, input_A) in (6, 7, 8, 9)


def _compute_assumption_k1(input_D: bool, input_C: bool, input_B: bool) -> bool:
    """Assumption 'k1': NOT (D AND (C OR B))"""
    return not (input_D and (input_C or input_B))


# ---- Public API ----


def output_greater_than_five(inputs: Mapping[str, bool], *, check_scope: bool = True) -> bool:
    """Decision output 'greater_than_five' (stable ID f_2d3893154eb6).

    'greater_than_five' := \u03a3m(D, C, B, A; 6, 7, 8, 9)

    Required inputs: 'D', 'C', 'B', 'A'; with check_scope=True also 'D', 'C', 'B' (read by the assumptions).
    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, ("D", "C", "B", "A"), check_scope)
    if check_scope:
        _require_in_scope(values)
    output_greater_than_five_value = _compute_output_greater_than_five(values["D"], values["C"], values["B"], values["A"])
    return output_greater_than_five_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: 'D', 'C', 'B', 'A'; with check_scope=True also 'D', 'C', 'B' (read by the assumptions).
    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, ("D", "C", "B", "A"), check_scope)
    if check_scope:
        _require_in_scope(values)
    output_greater_than_five_value = _compute_output_greater_than_five(values["D"], values["C"], values["B"], values["A"])
    return {
        "greater_than_five": output_greater_than_five_value,
    }


def assumption_k1(inputs: Mapping[str, bool]) -> bool:
    """Assumption 'k1' (stable ID f_180149c5249a).

    'k1' := NOT (D AND (C OR B))

    Description: The four bits encode a decimal digit 0 to 9 (BCD); codes 10 to 15 never occur.

    Required inputs: 'D', 'C', 'B'.
    Raises InputError for missing, undeclared, or non-bool inputs.
    """
    values = _checked_inputs(inputs, ("D", "C", "B"), False)
    assumption_k1_value = _compute_assumption_k1(values["D"], values["C"], values["B"])
    return assumption_k1_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: 7eb00dd03ae1ec07d2792c847f4e5db34288ea51c001af5f2977ef79fd88dcb3
-- Assumptions digest: 25076d78f029a36624a87032d35dc97d625d1c5ab40292fcb6e7c5f036915ed7
-- 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_095da454e794: D -> "in_D"
--   v_18ad16a71134: C -> "in_C"
--   v_7fc0ba5488b3: B -> "in_B"
--   v_b93ff9520200: A -> "in_A"
-- Output columns:
--   f_2d3893154eb6: greater_than_five -> "out_greater_than_five"
-- Assumptions (scope K; exported separately and never folded into an output):
--   f_180149c5249a: k1 -> "assumption_k1": NOT (D AND (C OR B))
--     The four bits encode a decimal digit 0 to 9 (BCD); codes 10 to 15 never occur.

-- ----------------------------------------------------------------------------------------------
-- 1. Expression fragments (parenthesised; non-NULL boolean inputs required)
-- ----------------------------------------------------------------------------------------------
--
-- [out_greater_than_five] output greater_than_five (stable ID f_2d3893154eb6)
--   greater_than_five := \u03a3m(D, C, B, A; 6, 7, 8, 9)
--   PRECONDITION: "in_D", "in_C", "in_B", "in_A" are non-NULL booleans.
--   (((NOT "in_D") AND "in_C" AND "in_B" AND (NOT "in_A")) OR ((NOT "in_D") AND "in_C" AND "in_B" AND "in_A") OR ("in_D" AND (NOT "in_C") AND (NOT "in_B") AND (NOT "in_A")) OR ("in_D" AND (NOT "in_C") AND (NOT "in_B") AND "in_A"))
--
-- [assumption_k1] assumption k1 (stable ID f_180149c5249a)
--   k1 := NOT (D AND (C OR B))
--   PRECONDITION: "in_D", "in_C", "in_B" are non-NULL booleans.
--   (NOT ("in_D" AND ("in_C" OR "in_B")))
--
-- [K] scope (conjunction of the assumptions):
--   (NOT ("in_D" AND ("in_C" OR "in_B")))
--

-- ----------------------------------------------------------------------------------------------
-- 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_D", "in_C", "in_B", "in_A") AS (
  -- tangibool:example-rows:begin
  VALUES
    (1, FALSE, FALSE, FALSE, FALSE),
    (2, FALSE, FALSE, FALSE, TRUE),
    (3, FALSE, FALSE, TRUE, FALSE),
    (4, FALSE, FALSE, TRUE, TRUE),
    (5, FALSE, TRUE, FALSE, FALSE),
    (6, FALSE, TRUE, FALSE, TRUE),
    (7, FALSE, TRUE, TRUE, FALSE),
    (8, FALSE, TRUE, TRUE, TRUE),
    (9, TRUE, FALSE, FALSE, FALSE),
    (10, TRUE, FALSE, FALSE, TRUE),
    (11, TRUE, FALSE, TRUE, FALSE),
    (12, TRUE, FALSE, TRUE, TRUE),
    (13, TRUE, TRUE, FALSE, FALSE),
    (14, TRUE, TRUE, FALSE, TRUE),
    (15, TRUE, TRUE, TRUE, FALSE),
    (16, TRUE, TRUE, TRUE, TRUE),
    (17, NULL::boolean, FALSE, FALSE, FALSE)
  -- tangibool:example-rows:end
),
checked AS (
  SELECT
    inputs.*,
    CASE
      WHEN "in_D" IS NULL OR "in_C" IS NULL OR "in_B" IS NULL OR "in_A" IS NULL THEN 'invalid_input'
      WHEN NOT (NOT ("in_D" AND ("in_C" OR "in_B"))) THEN 'out_of_scope'
      ELSE 'ok'
    END AS "status"
  FROM inputs
)
SELECT
  "row_id",
  "in_D",
  "in_C",
  "in_B",
  "in_A",
  "status",
  CASE WHEN "status" <> 'invalid_input' THEN (NOT ("in_D" AND ("in_C" OR "in_B"))) END AS "assumption_k1",
  CASE WHEN "status" = 'ok' THEN (((NOT "in_D") AND "in_C" AND "in_B" AND (NOT "in_A")) OR ((NOT "in_D") AND "in_C" AND "in_B" AND "in_A") OR ("in_D" AND (NOT "in_C") AND (NOT "in_B") AND (NOT "in_A")) OR ("in_D" AND (NOT "in_C") AND (NOT "in_B") AND "in_A")) END AS "out_greater_than_five"
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: 7eb00dd03ae1ec07d2792c847f4e5db34288ea51c001af5f2977ef79fd88dcb3
; Assumptions digest: 25076d78f029a36624a87032d35dc97d625d1c5ab40292fcb6e7c5f036915ed7
; 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_095da454e794: D -> in_D
;   v_18ad16a71134: C -> in_C
;   v_7fc0ba5488b3: B -> in_B
;   v_b93ff9520200: A -> in_A
;   f_2d3893154eb6: greater_than_five -> out_greater_than_five
;   f_180149c5249a: k1 -> assumption_k1

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

; ---- Inputs (declared order)
(declare-const in_D Bool) ; D
(declare-const in_C Bool) ; C
(declare-const in_B Bool) ; B
(declare-const in_A Bool) ; A

; ---- Outputs (dependencies first)
; output greater_than_five (stable ID f_2d3893154eb6): \u03a3m(D, C, B, A; 6, 7, 8, 9)
(define-fun out_greater_than_five () Bool (or (and (not in_D) in_C in_B (not in_A)) (and (not in_D) in_C in_B in_A) (and in_D (not in_C) (not in_B) (not in_A)) (and in_D (not in_C) (not in_B) in_A)))

; ---- Assumptions (the scope K; never folded into an output)
; assumption k1 (stable ID f_180149c5249a): NOT (D AND (C OR B))
;   The four bits encode a decimal digit 0 to 9 (BCD); codes 10 to 15 never occur.
(define-fun assumption_k1 () Bool (not (and in_D (or in_C in_B))))
; K: conjunction of the enabled, confirmed assumptions (true when there are none)
(define-fun K () Bool assumption_k1)

; ---- 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
greater_than_five = \sum m_{(D, C, B, A)}(6, 7, 8, 9)

The common slip

Forgetting that D alone covers eight cells, six of which are don't-cares. The group looks generous because the map is allowed to use them; on the original function D is true only on rows 8 and 9. The map's scope annotation records that the result holds within the assumption only.

Questions

Why not write D OR (C AND B) as the formula in the first place?

Because that formula and the minterm list disagree on codes 10 to 15, and the equivalence check would say so without the assumption. The page starts from the specification, states the assumption explicitly, and lets the map derive the short form with a label that says where it is valid.

Related

Guides

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.