How do I make a square rhombus in constructor?

http://www.algebra.com/cgi-bin/plot-formula.mpl?expression=drawing%28+160%2C+160%2C+-10%2C+10%2C+-10%2C+10%2C+line%28+-6%2C+-6%2C4%2C-6%29+%2C+line%28+-6%2C+-6%2C-4%2C4%29%2C+line%28+-4%2C4%2C2%2C4%29+%2C+line%28+2%2C+4%2C4%2C-6%29+%2Clocate%28+-6.5%2C-6.5%2Ca%29%2Clocate%28+4.5%2C-6.5%2Cb%29%2Clocate%28+2.5%2C4.5%2Cc%29%2Clocate%28-5.5%2C5%2Cd%29%29&x=0003


I want to make this shape but I don't know how.