---

name: evaluate-boolean-expression locale: caveman source_locale: en source_commit: 82c77053 fence_basis_commit: 82c77053 translator: "Julius Brussee homage — caveman" translation_date: "2026-04-24" description: > Evaluate and simplify Boolean expressions using truth tables, algebraic laws (De Morgan, distributive, absorption, idempotent, consensus), and Karnaugh maps for up to six variables. Use when you need to reduce a Boolean expression to its minimal sum-of-products or product-of-sums form, verify logical equivalence between two expressions, or prepare a minimized function for gate-level implementation. license: MIT allowed-tools: Read Grep Glob WebFetch WebSearch metadata: author: Philipp Thoss version: "1.0" domain: digital-logic complexity: basic language: multi tags: digital-logic, boolean-algebra, truth-tables, karnaugh-maps, simplification

Evaluate Boolean Expression

Shrink Boolean expression to smallest form: parse into canonical shape, build truth table, apply algebra laws, do Karnaugh map min (up to six vars), check new expression same logic as old.

When Use

• Shrink Boolean expression before map to logic gates
• Check two Boolean expressions are same logic
• Make smallest sum-of-products (SOP) or product-of-sums (POS) form
• Teach or review Boolean algebra rules and shrink moves
• Prep input for design-logic-circuit skill

Inputs

• Required: Boolean expression in any common form (e.g., A AND (B OR NOT C), A * (B + C'), A & (B | ~C))
• Required: Target form -- min SOP, min POS, or both
• Optional: Var order pick for Karnaugh map
• Optional: Don't-care cases (minterms or maxterms left undefined)
• Optional: Second expression to check same-logic against

Steps

Step 1: Parse and Normalize to Canonical Form

Turn input expression into standard inner shape:

1. Tokenize: Spot vars (single letters or short names), ops (AND, OR, NOT, XOR, NAND, NOR), and grouping (parens).
2. Set op notation: Pick one notation all through -- * for AND, + for OR, ' for NOT (complement), ^ for XOR.
3. Count vars: List all unique vars. Give each bit position (A = MSB, ... Z = LSB by default, or use given order).
4. Expand to canonical SOP: Expand expression to sum of all minterms by adding missing vars via rule X = X*(Y + Y').
5. Expand to canonical POS: Or expand to product of all maxterms via X = X + Y*Y'.

## Normalized Expression
- **Variables**: [A, B, C, ...]
- **Variable count**: [n]
- **Original expression**: [as given]
- **Canonical SOP (minterms)**: Sigma m(i, j, k, ...)
- **Canonical POS (maxterms)**: Pi M(i, j, k, ...)
- **Don't-care set**: d(i, j, ...) [if any]

Got: Expression turned to canonical SOP and/or POS with all minterms/maxterms listed clear and don't-care cases kept apart.

If fail: Expression has syntax errors or vague op precedence? Ask for clarity. Standard precedence: NOT (highest) > AND > XOR > OR (lowest). Var count over 6? Note K-map step will need Quine-McCluskey algorithm instead.

Step 2: Construct Truth Table

Build full truth table to pin function behavior over all input combos:

1. List rows: Make all 2^n input combos in binary count order (000, 001, 010, ...).
2. Evaluate output: For each row, plug values into old expression and compute output (0 or 1).
3. Mark don't-cares: If don't-care cases given, mark those rows with X not 0 or 1.
4. Cross-check with minterms: Confirm rows giving output 1 match minterm list from Step 1.

## Truth Table
| A | B | C | F |
|---|---|---|---|
| 0 | 0 | 0 | _ |
| 0 | 0 | 1 | _ |
| ... | ... | ... | ... |

Got: Full truth table with 2^n rows, outputs matching canonical form, don't-cares marked right.

If fail: Truth table clash with canonical form? Recheck expand in Step 1. Common slip: De Morgan's law mis-applied during canonical expand -- check each expand step one by one.

Step 3: Apply Algebraic Simplification

Shrink expression with Boolean algebra rules:

1. Identity and null laws: A + 0 = A, A * 1 = A, A + 1 = 1, A * 0 = 0.
2. Idempotent law: A + A = A, A * A = A.
3. Complement law: A + A' = 1, A * A' = 0.
4. Absorption law: A + A*B = A, A * (A + B) = A.
5. De Morgan's theorems: (A * B)' = A' + B', (A + B)' = A' * B'.
6. Distributive law: A * (B + C) = A*B + A*C, A + B*C = (A + B) * (A + C).
7. Consensus theorem: A*B + A'*C + B*C = A*B + A'*C (the B*C term is extra).
8. XOR shrink: Spot patterns like A*B' + A'*B = A ^ B.
9. Log each step: Write expression after each law apply, name law used.

## Algebraic Simplification Trace
1. Original: [expression]
2. Apply [law name]: [result]
3. Apply [law name]: [result]
...
n. Final algebraic form: [simplified expression]

Got: Step-by-step shrink with each law apply named, going to simpler expression. Trace is checkable proof of same-logic.

If fail: Expression won't shrink more but still feels not-min? Go to Step 4 (K-map). Algebra moves not guaranteed to find global min -- depend on order of law apply.

Step 4: Minimize via Karnaugh Map

Use K-map to find provably min SOP or POS form (for up to 6 vars):

1. Draw K-map: Set map using Gray code order on axes.
   • 2 variables: 2x2 grid
   • 3 variables: 2x4 grid
   • 4 variables: 4x4 grid
   • 5 variables: two 4x4 grids (stacked)
   • 6 variables: four 4x4 grids (stacked)
2. Fill cells: Place 1s (minterms), 0s (maxterms), Xs (don't-cares) in matching cells.
3. Group adjacent 1s: Form rectangular groups of 1, 2, 4, 8, 16, or 32 adjacent cells (powers of 2 only). Groups can wrap around edges. Add don't-cares to groups if they make group bigger.
4. Pull prime implicants: Each group gives product term. Vars constant across group stay in term; vars that change drop out.
5. Pick essential prime implicants: Spot minterms covered by only one prime implicant -- those implicants are essential.
6. Cover remaining minterms: Use fewest extra prime implicants to cover any uncovered minterms (Petrick's method if need).
7. Write min expression: Mix picked prime implicants into min SOP. For min POS, group 0s instead.

## K-map Result
- **Prime implicants**: [list with covered minterms]
- **Essential prime implicants**: [list]
- **Minimal SOP**: [expression]
- **Minimal POS**: [expression, if requested]
- **Literal count**: [number of literals in minimal form]

Got: Min SOP (and/or POS) with fewest literals, all prime implicants and essential prime implicants logged.

If fail: Groupings vague (many min covers exist)? List all same-value min forms. Var count over 6? Switch to Quine-McCluskey tabular method or Espresso heuristic; note the swap.

Step 5: Verify Simplified Expression Matches Original

Check same logic between shrunk and original expressions:

1. Truth table compare: Eval shrunk expression for all 2^n input combos and compare vs truth table from Step 2. Every non-don't-care row must match.
2. Algebraic proof (optional): Pull original from shrunk form (or reverse) using laws from Step 3.
3. Spot-check key cases: Check all-zeros input, all-ones input, and any input tied to tricky shrink step.
4. Log result: State whether same-logic holds and write final min form.

## Equivalence Verification
- **Method**: [truth table comparison / algebraic proof / both]
- **Mismatched rows**: [none, or list row numbers]
- **Verdict**: [Equivalent / Not equivalent]
- **Final minimal expression**: [the verified result]

Got: Shrunk expression matches original on all non-don't-care inputs. Final min form stated clear.

If fail: Any row mismatch? Trace error back through Steps 3-4. Common causes: wrong K-map grouping (non-rectangular or non-power-of-2 group), forget wrap-around adjacency, or slip grouping a 0 cell.

Validation

• All vars in original expression counted
• Canonical SOP/POS lists right minterms/maxterms
• Truth table has exactly 2^n rows with right outputs
• Don't-care cases handled right (added to groups but not in cover rule)
• Algebraic steps each name a specific law and can be checked one by one
• K-map uses Gray code order on both axes
• All groups in K-map are rectangular and power-of-2 size
• Essential prime implicants picked right
• Shrunk expression matches original on all non-don't-care inputs
• Final form has smallest number of literals

Pitfalls

• Wrong K-map adjacency: Forget leftmost and rightmost columns (and top and bottom rows) are adjacent in K-map. This wrap-around is key for finding biggest groups.
• Non-power-of-2 groups: Grouping 3 or 5 cells together. Every K-map group must have exactly 1, 2, 4, 8, 16, or 32 cells. Odd group not match any product term.
• Ignore don't-cares: Treat don't-care as 0s, not use them to grow groups. Don't-cares should join groups when doing so shrinks expression, but must not be needed for cover.
• Op precedence slip: Assume AND and OR have same precedence. Standard Boolean precedence is NOT > AND > OR. Misread A + B * C as (A + B) * C not A + (B * C) changes function full.
• Stop at algebra shrink: Algebra moves may find local min, not global min. Always cross-check with K-map (or Quine-McCluskey for >6 vars) to confirm smallest.
• Mix minterms and maxterms: Minterms are AND terms (product terms) in SOP; maxterms are OR terms (sum terms) in POS. Minterm m3 for 3 vars is A'BC; maxterm M3 is A+B'+C'.

See Also

• design-logic-circuit -- map shrunk expression to gate-level circuit
• argumentation -- structured logic reason that shares formal logic base