using internal node as a select line

Posted by nasserAlhouti on Mar 10, 2019; 4:30am
URL: http://nand2tetris-questions-and-answers-forum.52.s1.nabble.com/using-internal-node-as-a-select-line-tp4033017.html

For my ALU design I wanted to determine if a number is negative or positive by looking at its' last bit    
  // checks if zx is 1 then turns all bits to zeros  
Mux16(a=false,b=x,sel=zx,out=xzero);
// negates xzero
      Not16(in=xzero,out=notx);
// checks if nx is 1 then negates x
    Mux16(a=notx,b=xzero,sel=nx,out=xnegated);
// checks if x is negative

   Not16(in = xnegated , out = xnegated2);
   Inc16(in = xnegated2,out=xComplement);    
  Mux16(a=xComplement,b=xnegated,sel=xnegated[15],out=resultedX);

My issue lies in the fact that I can't access xnegated as its own bit in the bus of xnegated. As a result , I keep getting "sub bus of internal node may not be used". So is there a way around this issue??
I would like to apologies for my naming convention I couldn't think of any good names at the time.