Abstract:We establish a 1-1 correspondence between Valiant's character theory of match-gate/matchcircuit [13] and his signature theory of planarmatchgate/matchgrid [15], thus unifying the two theories in expressibility. In [3], we established a complete characterization of general matchgates, in terms of a set of useful Grassmann-Plucker identities. The 1-1 correspondence established in this paper gives a corresponding set of identities which completely characterizes planar-matchgates and their signatures. Applying this characterization we prove some negative results for holographic algorithms. On the positive side, we also give a polynomial time algorithm for a simultaneous node-edge deletion problem, using holographic algorithms. Finally we give characterizations of symmetric signatures realizable in the Hadamard basis.