/sci/ - Science & Math

>>9045743
The "typo" is a retraction. If [math]i\colon H\to G[/math] is the inclusion map, then [math]\varphi\circ i=1_H[/math], and this means it is a retraction. A consequence of this is that [math]G\congH\oplus N[/math] (or, some people denote that by = in this case). It's a real thing.