Quick question. E is a relation from S to C, and L is a relation from S to R.
E o L^-1 = { (r,c) ∈ RxC | ∃s∈S ( (r,s)∈L^-1 and (s,c)∈E) }

what motivates to change from (r,s)∈L^-1 to (s,r)∈L in the following step:
E o L^-1 = { (r,c) ∈ RxC | ∃s∈S ( (s,r)∈L and (s,c)∈E) }

Question

Quick question. E is a relation from S to C, and L is a relation from S to R. 
E o L^-1 = { (r,c) ∈  RxC | ∃s∈S ( (r,s)∈L^-1 and (s,c)∈E) }

what motivates to change from (r,s)∈L^-1 to (s,r)∈L in the following step:
E o L^-1 = { (r,c) ∈  RxC | ∃s∈S ( (s,r)∈L and (s,c)∈E) }

anonymous · Answer

I mean, i realize L and L^-1 are inverse of each other, but they're are not equivalent.