User:Prime.mover/Proof Structures

Ordinary proofs
...etc.

Topology Proofs
We examine each of the open set axioms in turn:

$(O1)$: Union of Open Sets
Let $\left \langle{U_i}\right \rangle_{i \in I}$ be a family of open sets of $T$.

Let $\displaystyle V = \bigcup_{i \mathop \in I} U_i$ be the union of $\left \langle{U_i}\right \rangle_{i \in I}$.



Hence $V$ is open by definition.

$(O2)$: Intersection of Open Sets
Let $U$ and $V$ be open sets of $T$.



Hence $U \cap V$ is open by definition.

$(O3)$: Set Itself


All the open set axioms are fulfilled, and the result follows.

Equivalence Proofs
Checking in turn each of the criteria for equivalence:

Reflexivity
So ... has been shown to be reflexive.

Symmetry
So ... has been shown to be symmetric.

Transitivity
So ... has been shown to be transitive.

... has been shown to be reflexive, symmetric and transitive.

Hence by definition it is an equivalence relation.

Ordering Proofs
Checking in turn each of the criteria for an ordering:

Reflexivity
So ... has been shown to be reflexive.

Transitivity
So ... has been shown to be transitive.

Antisymmetry
So ... has been shown to be antisymmetric.

... has been shown to be reflexive, transitive and antisymmetric.

Hence by definition it is an ordering.

Strict Ordering Proofs
Checking in turn each of the criteria for a strict ordering:

Antireflexivity
So ... has been shown to be antireflexive.

Transitivity
So ... has been shown to be transitive.

Asymmetry
So ... has been shown to be asymmetric.

... has been shown to be antireflexive, transitive and asymmetric.

Hence by definition it is a strict ordering.

Group Proofs
Taking the group axioms in turn:

G0: Closure
Thus ... and so ... is closed.

G1: Associativity
Thus ... is associative.

G2: Identity
Thus ... has an identity element.

G3: Inverses
Thus every element of ... has an inverse.

All the group axioms are thus seen to be fulfilled, and so ... is a group.

Ring Proofs
Taking the ring axioms in turn:

Proof by Mathematical Induction
Proof by induction:

For all $n \in \N_{> 0}$, let $P \left({n}\right)$ be the proposition:
 * $proposition_n$

$P \left({1}\right)$ is true, as this just says $proposition_1$.

Basis for the Induction
$P \left({2}\right)$ is the case:
 * $proposition_2$

which has been proved above.

This is our basis for the induction.

Induction Hypothesis
Now we need to show that, if $P \left({k}\right)$ is true, where $k \ge 2$, then it logically follows that $P \left({k+1}\right)$ is true.

So this is our induction hypothesis:
 * $proposition_k$

Then we need to show:
 * $proposition_{k+1}$

Induction Step
This is our induction step:

So $P \left({k}\right) \implies P \left({k+1}\right)$ and the result follows by the Principle of Mathematical Induction.

Therefore:
 * $proposition_n$

Tableau proofs
...etc.