# lexicographicallyPrecedes(_:by:)

Returns a Boolean value indicating whether the sequence precedes another sequence in a lexicographical (dictionary) ordering, using the given predicate to compare elements.

`func lexicographicallyPrecedes<OtherSequence>(_ other: OtherSequence, by areInIncreasingOrder: (Self.Element, Self.Element) throws -> Bool) rethrows -> Bool where OtherSequence : Sequence, Self.Element == OtherSequence.Element`

## Parameters

- other
A sequence to compare to this sequence.

- areInIncreasingOrder
A predicate that returns

`true`

if its first argument should be ordered before its second argument; otherwise,`false`

.

## Returns

`true`

if this sequence precedes `other`

in a dictionary ordering as ordered by `areInIncreasingOrder`

; otherwise, `false`

.

## Overview

The predicate must be a *strict weak ordering* over the elements. That is, for any elements `a`

, `b`

, and `c`

, the following conditions must hold:

`areInIncreasingOrder(a, a)`

is always`false`

. (Irreflexivity)If

`areInIncreasingOrder(a, b)`

and`areInIncreasingOrder(b, c)`

are both`true`

, then`areInIncreasingOrder(a, c)`

is also`true`

. (Transitive comparability)Two elements are

*incomparable*if neither is ordered before the other according to the predicate. If`a`

and`b`

are incomparable, and`b`

and`c`

are incomparable, then`a`

and`c`

are also incomparable. (Transitive incomparability)