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		 sorry, you are absoulely right!!
 I'm isreali... and i learn your course nand to tetris by onkine course in campus called "campus il" by Shion shoken and.. i wrote their the chip 'alu' without zr.... just the beggining.
 i add now all my implemented.
 this is one of the foles of nand to tetris, and i check it with the script nonstat.. that i got from you.
 
  This file is part of www.nand2tetris.org
 // and the book "The Elements of Computing Systems"
 // by Nisan and Schocken, MIT Press.
 // File name: projects/02/ALU.hdl
  /**
  * The ALU (Arithmetic Logic Unit).
  * Computes one of the following functions:
  * x+y, x-y, y-x, 0, 1, -1, x, y, -x, -y, !x, !y,
  * x+1, y+1, x-1, y-1, x&y, x|y on two 16-bit inputs, 
  * according to 6 input bits denoted zx,nx,zy,ny,f,no.
  * In addition, the ALU computes two 1-bit outputs:
  * if the ALU output == 0, zr is set to 1; otherwise zr is set to 0;
  * if the ALU output < 0, ng is set to 1; otherwise ng is set to 0.
  */
  // Implementation: the ALU logic manipulates the x and y inputs
 // and operates on the resulting values, as follows:
 // if (zx == 1) set x = 0        // 16-bit constant
 // if (nx == 1) set x = !x       // bitwise not
 // if (zy == 1) set y = 0        // 16-bit constant
 // if (ny == 1) set y = !y       // bitwise not
 // if (f == 1)  set out = x + y  // integer 2's complement addition
 // if (f == 0)  set out = x & y  // bitwise and
 // if (no == 1) set out = !out   // bitwise not
 // if (out == 0) set zr = 1
 // if (out < 0) set ng = 1
  CHIP ALU {
     IN  
         x[16], y[16],  // 16-bit inputs        
         zx, // zero the x input?
         nx, // negate the x input?
         zy, // zero the y input?
         ny, // negate the y input?
         f,  // compute out = x + y (if 1) or x & y (if 0)
         no; // negate the out output?
      OUT 
         out[16], // 16-bit output
         zr, // 1 if (out == 0), 0 otherwise
         ng; // 1 if (out < 0),  0 otherwise
      PARTS:
 Mux16(a=x,b=false,sel=zx,out=x1);
 Mux16(a=y,b=false,sel=zy,out=y1);
  Not16(in=x1,out=nx1);
 Mux16(a=x1,b=nx1,sel=nx,out=x2);
 Not16(in=y1,out=ny1);
 Mux16(a=y1,b=ny1,sel=ny,out=y2);
  Add16(a=x2,b=y2,out=aPlusB);
 And16(a=x2,b=y2,out=aAndb);
 Mux16(a=aAndb,b=aPlusB,sel=f,out=out0);
  Not16(in=out0,out=nout0);
 Mux16(a=out0,b=nout0,sel=no,out=out);
 
  
	
	
	
	 
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