AE4M33RZN, Fuzzy logic: Fuzzy relations

Theorem 234.
Let R, S and T be relations (defined over sets that “make sense”) The
following equations hold:
R ○ ∘ E = R, E ○ ∘ R = R (21)
(R ○ ∘ S) -1 = S -1 ○ ∘ R -1 (22)
R ○ ∘ (S ○ ∘ T) = (R ○ ∘ S) ○ ∘ T (23)