The following are exercises from The Four Pillars of Geometry; I'm not sure what they are stating, for example I don't know what the addition of prime (an apostrophe) to a line means. There are no examples or references.
3.6.5 Show that the reflections in lines $L$, $M$, and $N$ (in that order) have the same outcome as reflections in lines L', M', and $N$, where M' is perpendicular to $N$.
3.6.6 Next show that reflections in lines L', M', and $N$ have the same outcome as reflections in lines L', M'', and N' where M'' is parallel to L' and N' is perpendicular to M''.
3.6.7 Deduce from 3.6.6 that the combination of any three reflections is a glide reflection
I don't need to know how to do the problem, just what it's asking.