Prove
Proposition 1 ([Parity criterion]). Let Γ_A,Γ_B be finite loopless graphs…Theorem 1.1. There exist a finitely presented torsion-free group G and elements…Proposition
An ordinary letter lies on q+1 lines, so occurs at exactly (q+1)m=np vertices of A and (q+1)(m-1)=(n-v)p vertices of B . An extra letter belongs to four members of D , and therefore occurs 4a_m+1=(q+1)m times in A and 4b_m=(q+1)(m-1) times in B . This proves. The intersection of two ordinary parts has size q+1=129 when the lines agree and size one otherwise. For the extra parts, all intersections have even size except the intersection of the full seven-element set with itself. In fact, the possible even sizes are zero, two, and four. Only x_A has the full extra part, giving exactly the exception in. Finally, the possible sizes of S_x are 129 , 133 , and 136 .