Ken Monks
monks.scranton.edu
proveitmath.org
github.com/kenmonks/lurch

Getting Started with Lurch

Launch Lurch, Quick-start guides, and example contexts

Lurch is a free open source math editor that can check your reasoning.

Use Lurch

Open a new blank document in one of these mathematical contexts.

Lurch

No mathematical context at all. Best if you want to start completely from scratch.

New document

Lurch + Logic

Definitions, rules, and theorems for logic, quantifiers, and equality.

New document

Lurch + Set Theory + Logic

Elementary definitions and rules for naive set theory, including sets, sequences, and functions.

New document

Lurch + Real Numbers + Set Theory + Logic

Axioms for the real numbers, elementary algebra, naive set theory, and logic.

New document

Quick-Start Guides

Mastering the art of proof can take a lifetime, but getting started with Lurch is easy.

More Contexts

Open a new blank document in the student version of Lurch using the indicated context. They are organized by topic as follows.

Foundation: Logic and Equality

Each of the contexts in this section includes the rules defined in the contexts above it.

Propositional Logic

Use in Lurch

Defines and, or, not, implies, iff, and contradiction. view rules

Predicate Logic with Equality

Use in Lurch

Defines forall $\left(\forall\right)$, exists $\left(\exists\right)$ and equality $\left(=\right)$. view rules

Logic Theorems

Use in Lurch

Provides some common theorems about logic. (Includes: Equations) view rules

Peano Axioms, Induction, Number Theory, and Recursive Sequences

Each of the contexts in this section includes the rules defined in the contexts above it in this section, and all of the rules from the Foundation section above.

Natural Numbers

Use in Lurch

The Peano Axioms for the Natural Numbers. view rules

Number Theory Definitions

Use in Lurch

Defines less than $\left(\lt\right)$, divides $\left(\mid\right)$, prime, even and odd. view rules

Number Theory Theorems

Use in Lurch

Provides some useful theorems from Number Theory that are provable from the Peano Axioms. view rules

Sequences and Recursion

Use in Lurch

Defines summation $\left(\sum\right)$, Fibonacci numbers $\left(F_n\right)$, factorial $\left(!\right)$, multinomial coefficients $\left(m,n\right)$, binomial coefficients $\binom{n}{k}$ and exponentiation $\left(z^n\right)$. (Includes: Arithmetic in $\NN$) view rules

Set Theory, Real Numbers, Functions, and Relations

Each of the contexts in this section includes the rules defined in the contexts above it in this section, and all of the rules from the Foundation section above, but not the rules in the previous section.

Set Theory

Use in Lurch

Defines in $\left(\in\right)$, subset $\left(\subseteq\right)$, intersection $\left(\cap\right)$, union $\left(\cup\right)$, complement $\left('\right)$, set difference $\left(\setminus\right)$, power set $\left(\mathscr{P}\right)$, Cartesian product $\left(\times\right)$, finite set $\left\{ \ldots \right\}$, tuple $\langle\ldots\rangle$, Indexed Union $\left(\bigcup\right)$, Indexed Intersection $\left(\bigcap\right)$ and Set Builder notation $\left\{ z :\ldots \right\}$. view rules

Real Numbers

Use in Lurch

Defines the field axioms for the Real Numbers. view rules

Number Systems

Use in Lurch

Defines the sets $\NN$, $\ZZ$, and $\QQ$, and some basic theorems about them including induction, strong induction, and induction from $a$ in $\NN$. (Includes: Arithmetic in $\QQ$) view rules

Functions

Use in Lurch

Defines maps $\left(f\colon A \to B\right)$, function application $\left(f(x)\right)$, maps to $\left(\mapsto\right)$, image $\left(f(U)\right)$, identity map $\left(\text{id}_A\right)$ inverse image $\left(f^\text{inv}(U)\right)$, composition $\left(\circ\right)$, inverse function $\left(f^{-1}\right)$, injective, surjective and bijective.
(Includes: Algebra) view rules

Relations

Use in Lurch

Defines reflexive, symmetric, transitive, irreflexive, antisymmetric, total, partial order, strict partial order, total order, equivalence relation, partition, equivalence class $[a]$ view rules

Other Useful Contexts

Additional Rules. The following rules can be optionally added by the instructor to any particular document. They have no context of their own.

Equations

Use in Lurch

Defines a single ‘rule’ that enables Lurch to validate transitive chains of equalities without needing substitution, reflexivity, symmetry, or transitivity. Declares is to be a constant and provides a substitution rule for is. view rules

Arithmetic in the Natural Numbers

Use in Lurch

Allows the user to say 'by arithmetic' after an expression to try to justify it using a CAS. The expression can only contain natural number constants (e.g. $0$, $1$, $2$, etc) the operators $+$, $\cdot$, and $\text{^}$, and the relations $=$, $\neq$, $\leq$, and $\lt$. view rules

Arithmetic in the Integers

Use in Lurch

Allows the user to say 'by arithmetic' after an expression to try to justify it using a CAS. The expression can only contain natural number constants (e.g. $0$, $1$, $2$, etc) the operators $+$, $\cdot$, $\text{^}$, and $-$ and the relations $=$, $\neq$, $\leq$, and $\lt$. Exponents cannot be negative. view rules

Arithmetic in the Rationals

Use in Lurch

Allows the user to say 'by arithmetic' after an expression to try to justify it using a CAS. The expression can only contain natural number constants (e.g. $0$, $1$, $2$, etc) the operators $+$, $\cdot$, $\text{^}$, $-$, and $/$, and the relations $=$, $\neq$, $\leq$, and $\lt$. Exponents must be integers and you cannot divide by zero. view rules

Allows the user to say 'by algebra' after an equation to try to justify it using a CAS. There are little or no restrictions on what the equation can contain, so use at your own discretion. The identity is evaluated using Algebrite. This rule also validates inequalities that can be validated by the previous rule (Arithmetic in the Rationals). view rules examples.

Additional Cumulative Contexts. A few miscellaneous contexts that are either generically useful or illustrate using Lurch in some other branches of mathematics.

Functions, Sets, Equations, and Logic

Use in Lurch

Functions, Set Theory Theorems, Set Theory, Equations, Logic Theorems, Predicate Logic, Propositional Logic. view rules

Defines topological space, open, closed, and continuous (in a topological space). Includes the Functions, Sets, Equations, and Logic context. view rules

Linear Algebra

Use in Lurch

Defines linear, subspace, closed under addition, closed under multiplication, nonempty, vectors, vector addition, and scalar multiplication (in $\mathbb{R}^2$ and $\mathbb{R}^3$). Includes the Functions, Sets, Equations, and Logic context above. view rules examples.