53 Step 2 Claim: There exist C 0, C 1  S such that: C 0 and C 1 are neighbors ( C 1 = e'(C 0 ), e'=(p',m') ) D 0 = e(C 0 ) is D 1 = e(C 1 ) is (two configurations neighbors if one results from the other in a single step.) 0-valent 1-valent
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