The Nitty Gritty Details

Note that

nT l = alx + bly + clz + dlw
nT s = asx + bsy + csz + d

so we can write p' = (nTl)s − (nTs)l in component form as

x' = (alx + bly + clz + d) sx (asx + bsy + csz + d) lx
y' = (alx + bly + clz + d) sy (asx + bsy + csz + d) ly
z' = (alx + bly + clz + d) sz (asx + bsy + csz + d) lz
w' = (alx + bly + clz + d) (asx + bsy + csz + d) lw