case ({w, y})
  2’b00: aluout = a + b; //si 'w' e 'y' is 2’b00.
  2’b01: aluout = a - b;
  2’b10: aluout = a & b;
  default: $display(“Valores no válidos w,y = %b %b ”, w, y);
endcase    // muestra un error si w,y son 11, o contienen ‘x’s.