Definition：We say that a set is path-connected if every two opints in the set can be joined by a continuous path lying in the set.
example：[0,1] is path-connected.
for all points a and b in [0,1], there is a function f(x) = x such that f(a) = a, f(b) = b, f is continuous, so f is a continuous path.
2010-01-09 16:48:06 補充：
第一行打錯字 if every two "points"...