y−1=0\mathrm {y-1=0}y−1=0
y+1=0\mathrm {y+1=0}y+1=0
2x−y−1=0\mathrm {2x-y-1=0}2x−y−1=0
2x−y+1=0\mathrm {2x-y+1=0}2x−y+1=0
