NAND-only and NOR-only converter with equivalence proof
Rewrite an expression using only NAND gates, or only NOR gates, with the gate count and an exact proof that the construction computes the same function.
NAND and NOR are universal: every Boolean function can be built from either alone, which is why real chips are built from them. The converter first reduces your expression to AND, OR and NOT, then replaces each operator by its NAND-only (or NOR-only) construction: NOT A = NAND(A, A), A AND B = NAND(NAND(A, B), NAND(A, B)), A OR B = NAND(NAND(A, A), NAND(B, B)), and the dual rules for NOR. Each construction is a law on this site, with its own truth-table proof.
The result states the number of gates, the depth, and whether the engine's equivalence check against the original passed. Inverters can be built by feeding a signal to both inputs of a gate (the default) or by tying one input to a constant, which avoids duplicating a large subtree; the tool chooses the self-fed form unless it would exceed the size bound.
Gate counts are counts of the construction, not of an optimised circuit. The classic four-NAND XOR, for example, is smaller than the mechanical construction, and the worked example shows both with the proof that they are equivalent.
Limits
- Truth tables up to 12 inputs (4096 rows).
- Karnaugh maps up to 4 effective variables.
- Normal forms up to 4096 terms; expressions up to 20000 characters and 64 inputs.
How to write expressions
Write inputs as names (member, A, credit_ok) and combine them with AND, OR, NOT, XOR, -> (implies), <-> (if and only if), NAND(a, b), NOR(a, b), XNOR(a, b), or the symbols &&, ||, !, ∧, ∨, ¬, ·, +, ′. Minterm and maxterm forms work too: Σm(A, B, C; 1, 3), ΠM(A, B; 0). Precedence: NOT, then AND, then XOR, then OR, then ->, then <->; use parentheses to be explicit. =, ==, ^, &, | and ~ are rejected with a repair.
Example
f := (A AND B) OR C · output
Exact checks
Truth table (8 rows)
| # | A | B | C | f |
|---|---|---|---|---|
| 0 | FALSE | FALSE | FALSE | FALSE |
| 1 | FALSE | FALSE | TRUE | TRUE |
| 2 | FALSE | TRUE | FALSE | FALSE |
| 3 | FALSE | TRUE | TRUE | TRUE |
| 4 | TRUE | FALSE | FALSE | FALSE |
| 5 | TRUE | FALSE | TRUE | TRUE |
| 6 | TRUE | TRUE | FALSE | TRUE |
| 7 | TRUE | TRUE | TRUE | TRUE |
Plain-language reading
Beginnerf is true exactly when at least one of the following holds (both may hold):
1. both A and B are true
2. C is true
In every other case, f 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.
Intermediatef is true exactly when at least one of the following holds (both may hold):
1. both A and B are true
2. C is true
In every other case, f is false.
Advancedf is true exactly when at least one of the following holds (both may hold) [inclusive disjunction ∨]:
1. both A and B are true [conjunction ∧]
2. C is true
In every other case, f is false.
Formal notation: (A ∧ 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 C
Karnaugh map
- cells m6, m7
A AND B - cells m1, m3, m5, m7
C
Minterms and maxterms
f(A, B, C) = Σm(1, 3, 5, 6, 7)f(A, B, C) = ΠM(0, 2, 4)Variable order: A, B, C · 8 rows
Normal forms
Conjunctive normal form (CNF)
(A OR C) AND (B OR C)2 clauses, 4 literals · complete · Distribution ×1
Disjunctive normal form (DNF)
(A AND B) OR C2 terms, 3 literals · complete
NAND-only and NOR-only
NAND-only form
NAND(NAND(A, B), NAND(C, C))3 gates · verified equivalent on every row
NOR-only form
NOR(NOR(NOR(NOR(A, A), NOR(B, B)), C), NOR(NOR(NOR(A, A), NOR(B, B)), C))9 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: 010ec60fdb8f5a5f871b641088eb229ea454ef3f5842321021d5cfd745acaf4a
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:
'f' -> output_f(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})
# -> {'f': False}
model.output_f({'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_f",
]
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": "010ec60fdb8f5a5f871b641088eb229ea454ef3f5842321021d5cfd745acaf4a",
"assumptions_digest": "d58ee1ad38e23e5093e4baa1047b5ae70d6972e08f555e34ac3fa16df63c4a78",
"primary_output": "f",
"unused_inputs": (),
"subcircuits": (),
}
# Stable ID -> generated identifier (reversible mapping; names are exact, escaped strings).
IDENTIFIER_MAP = {
"v_731f2d81b144": {"kind": "input", "name": "A", "identifier": "input_A"},
"v_840db62aab93": {"kind": "input", "name": "B", "identifier": "input_B"},
"v_f560fae17b28": {"kind": "input", "name": "C", "identifier": "input_C"},
"f_38cb46cc6539": {"kind": "output", "name": "f", "identifier": "output_f"},
}
INPUT_NAMES = ("A", "B", "C")
OUTPUT_NAMES = ("f",)
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_f(input_A: bool, input_B: bool, input_C: bool) -> bool:
"""Decision output 'f': (A AND B) OR C"""
return (input_A and input_B) or input_C
# ---- Public API ----
def output_f(inputs: Mapping[str, bool], *, check_scope: bool = True) -> bool:
"""Decision output 'f' (stable ID f_38cb46cc6539).
'f' := (A AND B) OR 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_f_value = _compute_output_f(values["A"], values["B"], values["C"])
return output_f_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_f_value = _compute_output_f(values["A"], values["B"], values["C"])
return {
"f": output_f_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: 010ec60fdb8f5a5f871b641088eb229ea454ef3f5842321021d5cfd745acaf4a
-- 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_731f2d81b144: A -> "in_A"
-- v_840db62aab93: B -> "in_B"
-- v_f560fae17b28: C -> "in_C"
-- Output columns:
-- f_38cb46cc6539: f -> "out_f"
-- 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_f] output f (stable ID f_38cb46cc6539)
-- f := (A AND B) OR C
-- PRECONDITION: "in_A", "in_B", "in_C" are non-NULL booleans.
-- (("in_A" AND "in_B") OR "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_C") END AS "out_f"
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: 010ec60fdb8f5a5f871b641088eb229ea454ef3f5842321021d5cfd745acaf4a ; 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_731f2d81b144: A -> in_A ; v_840db62aab93: B -> in_B ; v_f560fae17b28: C -> in_C ; f_38cb46cc6539: f -> out_f (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 f (stable ID f_38cb46cc6539): (A AND B) OR C (define-fun out_f () Bool (or (and in_A 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
f = \left(A \cdot B\right) + C
Questions
Which is better, NAND or NOR?
They are equally expressive. The gate count for a given function usually differs between the two, and the comparison page shows the counts side by side for the same rule.
Why is the NAND form so much longer than my expression?
Each AND or OR becomes two or three NANDs and each NOT becomes one, and nothing is shared between gates in the textual form. In a circuit, repeated subexpressions are built once; the text cannot show that sharing.
Related
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
- CNF and DNF converter: conjunctive and disjunctive normal forms, minterms and maxterms
- Logical equivalence checker: two expressions, exact verdict, counterexample
- Argument validity checker: premises, conclusion, counterexample or proof
- Logic circuit generator: Boolean expression to gate diagram (SVG)
- Boolean expression to Python, SQL, SMT-LIB and LaTeX
Practice
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
- CNF and DNF converter: conjunctive and disjunctive normal forms, minterms and maxterms
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.