Majority of three with NAND gates only
A hand-wired NAND circuit for majority of three, NAND(NAND(A, B), NAND(NAND(A, C), NAND(B, C))), checked against (A AND B) OR (A AND C) OR (B AND C). The equivalence check fails on six of eight rows; the engine's own 9-gate construction is the verified one.
Majority is true when at least two of A, B and C are true, and the reference formula lists the three pairs. A NAND-only version of an OR of ANDs is a NAND of NANDs, and the circuit on this page is an attempt at that: NAND(A, B) for one pair, a nested NAND for the other two, and an outer NAND to combine them. The engine's reading of the reference says majority holds exactly when at least one of the three pairs is wholly true, rows 3, 5, 6 and 7, Σm(3, 5, 6, 7).
The equivalence check is violated: the counterexample is A = FALSE, B = FALSE, C = FALSE, where majority is false and with_nands is true. The table marks six differing rows, 0 through 5; the two columns agree only on rows 6 and 7. The nested NAND of the second and third pairs computes their OR, so the outer gate combines the wrong polarity. The engine's NAND-only converter builds the reference correctly, 9 gates, replayed against the table and verified. The reference's other results are those of the majority page: no simplification law applies, and the CNF and the map are as there.
This page is on the site because the failure is the lesson. A NAND circuit that looks right, uses plausible gates and has a sensible count can still compute a different function, and only a row-by-row check finds it; here it is the all-false row, the first test anyone should run. The thing to watch is nesting depth: each extra level of NAND flips polarity, and a design that forgets one flip fails on most rows while agreeing on the ones a quick test is likely to try.
majority := (A AND B) OR (A AND C) OR (B AND C) · outputwith_nands := NAND(NAND(A, B), NAND(NAND(A, C), NAND(B, C))) · output
Exact checks
Truth table (8 rows)
| # | A | B | C | majority | with_nands |
|---|---|---|---|---|---|
| 0 | FALSE | FALSE | FALSE | FALSE | TRUE |
| 1 | FALSE | FALSE | TRUE | FALSE | TRUE |
| 2 | FALSE | TRUE | FALSE | FALSE | TRUE |
| 3 | FALSE | TRUE | TRUE | TRUE | FALSE |
| 4 | TRUE | FALSE | FALSE | FALSE | TRUE |
| 5 | TRUE | FALSE | TRUE | TRUE | FALSE |
| 6 | TRUE | TRUE | FALSE | TRUE | TRUE |
| 7 | TRUE | TRUE | TRUE | TRUE | TRUE |
Plain-language reading
Beginnermajority is true exactly when at least one of the following holds (several may hold):
1. both A and B are true
2. both A and C are true
3. both B and C are true
In every other case, majority 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.
Intermediatemajority is true exactly when at least one of the following holds (several may hold):
1. both A and B are true
2. both A and C are true
3. both B and C are true
In every other case, majority is false.
Advancedmajority is true exactly when at least one of the following holds (several may hold) [inclusive disjunction ∨]:
1. both A and B are true [conjunction ∧]
2. both A and C are true [conjunction ∧]
3. both B and C are true [conjunction ∧]
In every other case, majority is false.
Formal notation: (A ∧ B) ∨ (A ∧ C) ∨ (B ∧ C)
Logic diagram
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.
(A AND B) OR (A AND C) OR (B AND C)
Karnaugh map
- cells m6, m7
A AND B - cells m5, m7
A AND C - cells m3, m7
B AND C
Minterms and maxterms
majority(A, B, C) = Σm(3, 5, 6, 7)majority(A, B, C) = ΠM(0, 1, 2, 4)Variable order: A, B, C · 8 rows
Normal forms
Conjunctive normal form (CNF)
(A OR B) AND (A OR C) AND (B OR C)3 clauses, 6 literals · complete · Distribution ×2, Absorption ×2, Idempotence ×1
Disjunctive normal form (DNF)
(A AND B) OR (A AND C) OR (B AND C)3 terms, 6 literals · complete
NAND-only and NOR-only
NAND-only form
NAND(NAND(NAND(NAND(A, B), NAND(A, C)), NAND(NAND(A, B), NAND(A, C))), NAND(B, C))9 gates · verified equivalent on every row
NOR-only form
NOR(NOR(NOR(NOR(NOR(NOR(A, A), NOR(B, B)), NOR(NOR(A, A), NOR(C, C))), NOR(NOR(NOR(A, A), NOR(B, B)), NOR(NOR(A, A), NOR(C, C)))), NOR(NOR(B, B), NOR(C, C))), NOR(NOR(NOR(NOR(NOR(A, A), NOR(B, B)), NOR(NOR(A, A), NOR(C, C))), NOR(NOR(NOR(A, A), NOR(B, B)), NOR(NOR(A, A), NOR(C, C)))), NOR(NOR(B, B), NOR(C, C))))39 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: 1ded6f5fbcfa0e0edcb1bb10b22280045cdc3756c7e37e82ec1b3a5ce18edd65
Assumptions digest: d58ee1ad38e23e5093e4baa1047b5ae70d6972e08f555e34ac3fa16df63c4a78
Inputs (dict keys, declared order) and generated parameter names:
'A' -> input_A
'B' -> input_B
'C' -> input_C
Outputs (declared order) and their functions:
'majority' -> output_majority(inputs)
'with_nands' -> output_with_nands(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, 'B': False, 'C': False})
# -> {'majority': False, 'with_nands': True}
model.output_majority({'A': False, 'B': False, 'C': False})
# -> False
model.evaluate({'A': 1, 'B': False, 'C': 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_majority",
"output_with_nands",
]
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": "1ded6f5fbcfa0e0edcb1bb10b22280045cdc3756c7e37e82ec1b3a5ce18edd65",
"assumptions_digest": "d58ee1ad38e23e5093e4baa1047b5ae70d6972e08f555e34ac3fa16df63c4a78",
"primary_output": "majority",
"unused_inputs": (),
"subcircuits": (),
}
# Stable ID -> generated identifier (reversible mapping; names are exact, escaped strings).
IDENTIFIER_MAP = {
"v_7d0a4f462d4c": {"kind": "input", "name": "A", "identifier": "input_A"},
"v_4b0198ebb4fa": {"kind": "input", "name": "B", "identifier": "input_B"},
"v_34c4c8cd22b7": {"kind": "input", "name": "C", "identifier": "input_C"},
"f_579e96a00edb": {"kind": "output", "name": "majority", "identifier": "output_majority"},
"f_de908012dd0c": {"kind": "output", "name": "with_nands", "identifier": "output_with_nands"},
}
INPUT_NAMES = ("A", "B", "C")
OUTPUT_NAMES = ("majority", "with_nands")
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_majority(input_A: bool, input_B: bool, input_C: bool) -> bool:
"""Decision output 'majority': (A AND B) OR (A AND C) OR (B AND C)"""
return (input_A and input_B) or (input_A and input_C) or (input_B and input_C)
def _compute_output_with_nands(input_A: bool, input_B: bool, input_C: bool) -> bool:
"""Decision output 'with_nands': NAND(NAND(A, B), NAND(NAND(A, C), NAND(B, C)))"""
return not ((not (input_A and input_B)) and (not ((not (input_A and input_C)) and (not (input_B and input_C)))))
# ---- Public API ----
def output_majority(inputs: Mapping[str, bool], *, check_scope: bool = True) -> bool:
"""Decision output 'majority' (stable ID f_579e96a00edb).
'majority' := (A AND B) OR (A AND C) OR (B AND C)
Required inputs: 'A', 'B', 'C'.
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", "B", "C"), check_scope)
if check_scope:
_require_in_scope(values)
output_majority_value = _compute_output_majority(values["A"], values["B"], values["C"])
return output_majority_value
def output_with_nands(inputs: Mapping[str, bool], *, check_scope: bool = True) -> bool:
"""Decision output 'with_nands' (stable ID f_de908012dd0c).
'with_nands' := NAND(NAND(A, B), NAND(NAND(A, C), NAND(B, C)))
Required inputs: 'A', 'B', 'C'.
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", "B", "C"), check_scope)
if check_scope:
_require_in_scope(values)
output_with_nands_value = _compute_output_with_nands(values["A"], values["B"], values["C"])
return output_with_nands_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', 'B', 'C'.
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", "B", "C"), check_scope)
if check_scope:
_require_in_scope(values)
output_majority_value = _compute_output_majority(values["A"], values["B"], values["C"])
output_with_nands_value = _compute_output_with_nands(values["A"], values["B"], values["C"])
return {
"majority": output_majority_value,
"with_nands": output_with_nands_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: 1ded6f5fbcfa0e0edcb1bb10b22280045cdc3756c7e37e82ec1b3a5ce18edd65
-- 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_7d0a4f462d4c: A -> "in_A"
-- v_4b0198ebb4fa: B -> "in_B"
-- v_34c4c8cd22b7: C -> "in_C"
-- Output columns:
-- f_579e96a00edb: majority -> "out_majority"
-- f_de908012dd0c: with_nands -> "out_with_nands"
-- 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_majority] output majority (stable ID f_579e96a00edb)
-- majority := (A AND B) OR (A AND C) OR (B AND C)
-- PRECONDITION: "in_A", "in_B", "in_C" are non-NULL booleans.
-- (("in_A" AND "in_B") OR ("in_A" AND "in_C") OR ("in_B" AND "in_C"))
--
-- [out_with_nands] output with_nands (stable ID f_de908012dd0c)
-- with_nands := NAND(NAND(A, B), NAND(NAND(A, C), NAND(B, C)))
-- PRECONDITION: "in_A", "in_B", "in_C" are non-NULL booleans.
-- (NOT ((NOT ("in_A" AND "in_B")) AND (NOT ((NOT ("in_A" AND "in_C")) AND (NOT ("in_B" AND "in_C"))))))
--
-- ----------------------------------------------------------------------------------------------
-- 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", "in_B", "in_C") 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_A" IS NULL OR "in_B" IS NULL OR "in_C" IS NULL THEN 'invalid_input'
ELSE 'ok'
END AS "status"
FROM inputs
)
SELECT
"row_id",
"in_A",
"in_B",
"in_C",
"status",
CASE WHEN "status" = 'ok' THEN (("in_A" AND "in_B") OR ("in_A" AND "in_C") OR ("in_B" AND "in_C")) END AS "out_majority",
CASE WHEN "status" = 'ok' THEN (NOT ((NOT ("in_A" AND "in_B")) AND (NOT ((NOT ("in_A" AND "in_C")) AND (NOT ("in_B" AND "in_C")))))) END AS "out_with_nands"
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: 1ded6f5fbcfa0e0edcb1bb10b22280045cdc3756c7e37e82ec1b3a5ce18edd65 ; 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_7d0a4f462d4c: A -> in_A ; v_4b0198ebb4fa: B -> in_B ; v_34c4c8cd22b7: C -> in_C ; f_579e96a00edb: majority -> out_majority ; f_de908012dd0c: with_nands -> out_with_nands (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 (declare-const in_B Bool) ; B (declare-const in_C Bool) ; C ; ---- Outputs (dependencies first) ; output majority (stable ID f_579e96a00edb): (A AND B) OR (A AND C) OR (B AND C) (define-fun out_majority () Bool (or (and in_A in_B) (and in_A in_C) (and in_B in_C))) ; output with_nands (stable ID f_de908012dd0c): NAND(NAND(A, B), NAND(NAND(A, C), NAND(B, C))) (define-fun out_with_nands () Bool (not (and (not (and in_A in_B)) (not (and (not (and in_A in_C)) (not (and in_B in_C))))))) ; ---- 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
majority = \left(A \cdot B\right) + \left(A \cdot C\right) + \left(B \cdot C\right)
with_nands = \overline{\overline{A \cdot B} \cdot \overline{\overline{A \cdot C} \cdot \overline{B \cdot C}}}The common slip
Checking a NAND design only on the all-true row. With A = TRUE, B = TRUE, C = TRUE the hand-wired circuit and the reference both give TRUE, as on row 6. The disagreement starts at A = FALSE, B = FALSE, C = FALSE, where majority is FALSE and the circuit TRUE; six rows differ in all.
Questions
What is the correct NAND-only majority?
The converter's construction with 9 gates, shown on the page and verified on all eight rows. In words: NAND each pair, then NAND the results, with tied-input NANDs where the construction needs an inversion. A hand design can be shorter, but it must be checked the same way.
Why does the engine not fix the circuit?
The engine computes and reports; it does not decide what you meant. It shows the counterexample, replays it through the independent evaluator, and lists the differing rows. Choosing the corrected circuit is the designer's job, and the converter's verified construction is a safe starting point.
Related
Operators and gates
- AND gate: truth table for 2, 3 and 4 inputs, symbol and expression
- OR gate: truth table for 2, 3 and 4 inputs, inclusive or explained
- NAND gate: truth table for 2, 3 and 4 inputs, universal gate
Tools
- Truth table generator: any Boolean expression, up to 12 variables, with intermediate columns
- Boolean algebra calculator and simplifier with steps (every law named and verified)
- Karnaugh map solver: 2 to 4 variables, groups, SOP and POS, don’t-cares from assumptions
See also
- Majority of three (2-out-of-3 voting): truth table, K-map and NAND form
- XOR with four NAND gates, verified equivalent
- NAND-only and NOR-only converter with equivalence proof
- Logical equivalence checker: two expressions, exact verdict, counterexample
- Counterexample in logic: meaning and examples
- NAND-only and NOR-only design exercises with answers
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.