# Definition:Increasing

(Redirected from Definition:Order-Preserving)

## Definition

### Ordered Sets

Let $\struct {S, \preceq_1}$ and $\struct {T, \preceq_2}$ be ordered sets.

Let $\phi: S \to T$ be a mapping.

Then $\phi$ is increasing if and only if:

$\forall x, y \in S: x \preceq_1 y \implies \map \phi x \preceq_2 \map \phi y$

Note that this definition also holds if $S = T$.

### Real Functions

This definition continues to hold when $S = T = \R$.

Let $f$ be a real function.

Then $f$ is increasing if and only if:

$x \le y \implies \map f x \le \map f y$

### Sequences

Let $\struct {S, \preceq}$ be a totally ordered set.

Let $A$ be a subset of the natural numbers $\N$.

Then a sequence $\sequence {a_k}_{k \mathop \in A}$ of terms of $S$ is increasing if and only if:

$\forall j, k \in A: j < k \implies a_j \preceq a_k$