Stack Exchange network consists of 183 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.
It is not always a monomorphism. Let X be R^2 \setminus { (x,y) : x^2 + y^2 <=< 1 }. Then X has fundamental group the integers, but Y is contractible.
It is not always a monomorphism. Let X be R^2 \setminus { (x,y) : x^2 + y^2 <= 1 }. Then X has fundamental group the integers, but Y is contractible.
It is not always a monomorphism. Let X be R^2 \setminus { (x,y) : x^2 + y^2 < 1 }. Then X has fundamental group the integers, but Y is contractible.
