(\x.\y.\z.xz(yz))(\x.\y.x)(\x.\y.x)
Alpha rename:
(\x.\y.\z.xz(yz))(\a.\b.a)(\c.\d.c)
Substitute (\a.\b.a) for x:
(\y.\z.(\a.\b.a)z(yz))(\c.\d.c) 
Substitute z for a:
(\y.\z.(\b.z)(yz))(\c.\d.c)
Substitute (yz) for b:
(\y.\z.z)(\c.\d.c)
Substitute (\c.\d.c) for y:
\z.z