or more invariantly by the quotient C(S)/S after phases are removed.
For P=Ea†Eb, there are three cases. If P∈S, it acts asascalar on the code. If P∈/C(S), it anticommutes with a stabilizer and ΠLPΠL=0. If P∈C(S)∖S, it acts asa nontrivial logical operator and is not proportional to the identity. Therefore
the KL conditions hold⟺Ea†Eb∈/LOSfor every a,b.