Editing Second quantization (section)

===== Examples =====
Hereinafter the tensor symbol <math>\otimes</math> between single-particle states is omitted for simplicity. Take the state <math>|1_1,1_2\rangle=(\psi_1\psi_2-\psi_2\psi_1)/\sqrt{2}</math>, attempt to create one more fermion on the occupied <math>\psi_1</math> state will quench the whole many-body wave function,
:<math>\begin{array}{rl}c_1^\dagger|1_1,1_2\rangle=&\frac{1}{\sqrt{2}}(c_1^\dagger\psi_1\psi_2-c_1^\dagger\psi_2\psi_1)\\=&\frac{1}{\sqrt{2}}\left(\frac{1}{\sqrt{3}}\psi_1\otimes_-\psi_1\psi_2-\frac{1}{\sqrt{3}}\psi_1\otimes_-\psi_2\psi_1\right)\\=&\frac{1}{\sqrt{2}}\left(\frac{1}{\sqrt{3}}(\psi_1\psi_1\psi_2-\psi_1\psi_1\psi_2+\psi_1\psi_2\psi_1)-\frac{1}{\sqrt{3}}(\psi_1\psi_2\psi_1-\psi_2\psi_1\psi_1+\psi_2\psi_1\psi_1)\right)\\=&0.\end{array}</math>
Annihilate a fermion on the <math>\psi_2</math> state,
take the state <math>|1_1,1_2\rangle=(\psi_1\psi_2-\psi_2\psi_1)/\sqrt{2}</math>,
:<math>\begin{array}{rl}c_2|1_1,1_2\rangle=&\frac{1}{\sqrt{2}}(c_2\psi_1\psi_2-c_2\psi_2\psi_1)\\=&\frac{1}{\sqrt{2}}\left(\frac{1}{\sqrt{2}}\psi_2\oslash_-\psi_1\psi_2-\frac{1}{\sqrt{2}}\psi_2\oslash_-\psi_2\psi_1\right)\\=&\frac{1}{\sqrt{2}}\left(\frac{1}{\sqrt{2}}(0-\psi_1)-\frac{1}{\sqrt{2}}(\psi_1-0)\right)\\=&-\psi_1\\=&-|1_1,0_2\rangle.\end{array}</math>
The minus sign (known as the fermion sign) appears due to the anti-symmetric property of the fermion wave function.