is primary key( foo, bar) the same as primary key ( foo ) with a ‘set' of bars?

[Kevin Burton]

I think the two tables are the same.  Correct?

create table foo (

    source text,
    target text,
    primary key( source, target )
)


vs

create table foo (

    source text,
    target set<text>,
    primary key( source )
)

… meaning that the first one, under the covers is represented the same as
the second.  As a slice.

Am I correct?

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