null homotopic造句

例句與造句

1. If for some " i " all maps are null homotopic, then the group ? " i " consists of one element, and is called the trivial group.
2. Just as one point is distinguished, so one class is distinguished : all maps ( or curves ) homotopic to the constant map " S " 1 ?! " x " are called null homotopic.
3. The null homotopic class acts as the identity of the group addition, and for " X " equal to " S " " n " ( for positive " n " )  the homotopy groups of spheres  the groups are finitely generated.
4. It's difficult to find null homotopic in a sentence. 用null homotopic造句挺難的