A Lemma for Color Switching on the Square Lattice

We consider 2d critical Bernoulli percolation on the square lattice. We prove an approximate color-switching lemma comparing k arm probabilities for different polychromatic color sequences. This result is well-known for site percolation on the triangular lattice in [Nolin08]. To handle the complications arising from the dual lattice, we introduce a shifting transformation to convert arms between the primal and the dual lattices.