q in (-oo:+oo)
2/3 = (1/3)*q // - (1/3)*q
2/3-((1/3)*q) = 0
ddddddddd
d d
d d
(-1/3)*q+2/3 = 0 d d
d d
2/3-1/3*q = 0 // - 2/3 d d
d d
-1/3*q = -2/3 // : -1/3 d d
d d
q = -2/3/(-1/3) ddddddd dddddddd
dd dd
q = 2 dd dd
dd dddd dd
q = 2 dddddddddd dddddddddddd