# starts(with:by:)

Returns a Boolean value indicating whether the initial elements of the sequence are equivalent to the elements in another sequence, using the given predicate as the equivalence test.

`func starts<PossiblePrefix>(with possiblePrefix: PossiblePrefix, by areEquivalent: (Self.Element, PossiblePrefix.Element) throws -> Bool) rethrows -> Bool where PossiblePrefix : Sequence`

## Parameters

- possibleprefix
A sequence to compare to this sequence.

- areequivalent
A predicate that returns

`true`

if its two arguments are equivalent; otherwise,`false`

.

## Returns

`true`

if the initial elements of the sequence are equivalent to the elements of `possiblePrefix`

; otherwise, `false`

. If `possiblePrefix`

has no elements, the return value is `true`

.

## Overview

The predicate must be a *equivalence relation* over the elements. That is, for any elements `a`

, `b`

, and `c`

, the following conditions must hold:

`areEquivalent(a, a)`

is always`true`

. (Reflexivity)`areEquivalent(a, b)`

implies`areEquivalent(b, a)`

. (Symmetry)If

`areEquivalent(a, b)`

and`areEquivalent(b, c)`

are both`true`

, then`areEquivalent(a, c)`

is also`true`

. (Transitivity)