Let X:=[0,1]×[0,1] (Unit Square) and let Y=T×T (Torus). Verify the following:
(1) If s1−s2=±1 then define (s1,t1)∼(s2,t2) iff t1=t2. If t1−t2=±1 then define (s1,t1)∼(s2,t2) iff s1=s2. If (s1,t1),(s2,t2)∈[0,1]×[0,1] then (s1,t1)∼(s2,t2) provided s1=s2 and t1=t2. Then ∼ defines an equivalence relation on X.
(2) f:X→Y given by f(s,t)=(e2πis,e2πit) is a continuous surjection. Conclude that X/∼ and Y are homeomorphic.