Partial rule composition. (a) Commutative diagram of the composition (L, K, R) = (L2, K2, R2) ∘ (L1, K1, R1), with arrows denoting subgraph isomorphisms. Not shown is that L2 is the disjoint union of and , i.e., ). Additionally, , and . (b) Illustration of the subgraph relations of a partial composition: is a subgraph of R1, R2 is a subgraph of the resulting right side R.