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Left quotient operator on regular expressions
Given two regular languages L1 and L2, we can define the left language quotient operations as L2\lL1:={v ∣ ∃u,uv∈L1∧u∈L2}. The Brzozowski derivative is a special case of the left quotient by a singleton language: {c}\lL1:={v ∣ cv∈L1}. This leads to the following question: is there a purely inductive definition of the left quotient operation on regular expressions? i.e. a function f:RE×RE→RE s.t. L(f(R2,R1))=L(R2)\lL(R1).