identify the error in Mani's proof that 2=1. justify

let x and y be equal qualities

step 1: x=y

step 2: x^{2 = xy}

step 3: x² -y² = xy-y²

step 4 : )x-y) (x+y) = y(x-y)

step 5: x+y = y

step 6: y+y = Y

step 7: 2y = y

step 8: 2=1