Semantics question regarding the General Computation Model

[Glenn Osborne]

The General Computation Model of the CTM book shows the following simplification from Construct 1 to Construct 2. I don't see how Construct 2 can work without a thread. What am I missing?

Construct 1:

proc {Ints N Xs}

    thread P in

        {WaitNeeded Xs}

        proc {P Xs} Ys in Xs=N|Ys {Ints N+1 Ys} end

        {P Xs}

    end

end

Van Roy, Peter; Seif Haridi (2004-03-01). Concepts, Techniques, and Models of Computer Programming (Page 797). MIT Press. Kindle Edition. 

Construct 2:

proc {Ints N Xs}

Ys in

    {WaitNeeded Xs}

    Xs=N|Ys

    {Ints N+1 Ys}

end

Van Roy, Peter; Seif Haridi (2004-03-01). Concepts, Techniques, and Models of Computer Programming (Page 798). MIT Press. Kindle Edition.