EEG	electroencephalographic
BCI	brain–computer interface
OpenBCI	open source brain–computer interface
GUI	graphical user interface
ADC	analog-to-digital converter
Ag-AgCl electrode	silver chloride electrode
$\mathit{R}$	set of real numbers
$\mathit{Z}$	set of integers
$\mathit{N}$	set of natural numbers
$\mathsf{\Omega }$	set of elementary events
N	number of electrodes (leads) on the surface of the operator’s head
M	number of experiments of the same type carried out for one operator
$\gamma$	parameter denoting (marking) an invariant from the group of invariants of vectors of cyclic rhythmically connected random processes
$\mathbf{E}\left\{·\right\}$	mathematical expectation operator
${\mathsf{\Theta }}_N(\omega ,t)$	vector of cyclic rhythmically connected random processes
${\xi }_i(\omega ,t)$	ith component of vector of cyclic rhythmically connected random processes
$T(t,n)$	rhythm function of vector of cyclic rhythmically connected random processes
${\mathsf{\Theta }}_{N_{\omega }}\left(t\right)$	realization of vector of cyclic rhythmically connected random processes
$F_{k_{{\xi }_{i_1}\dots {\xi }_{i_k}}}(x_1,\dots ,x_k;t_1,\dots ,t_k)$	compatible k-dimensional distribution function of vector of cyclic rhythmically connected random processes
$f_{k_{{\xi }_{i_1}\dots {\xi }_{i_k}}}(u_1,\dots ,u_k;t_1,\dots ,t_k)$	compatible k-dimensional characteristic function of vector of cyclic rhythmically connected random processes
$C_{p_{{\xi }_{i_1}\dots {\xi }_{i_k}}}(t_1,\dots ,t_k)$	mixed initial moment function of vector of cyclic rhythmically connected random processes
$R_{p_{{\xi }_{i_1}\dots {\xi }_{i_k}}}(t_1,\dots ,t_k)$	mixed central moment function of vector of cyclic rhythmically connected random processes
${\mathit{W}}_{m,1}$	time area that corresponds to state of operator’s passivity in mth cycle of electroencephalographic signal
${\mathit{W}}_{m,2}$	time area that corresponds to state of operator’s activity in mth cycle of electroencephalographic signal
${\mathit{W}}_{c_m}$	time area of definition of mth cycle of electroencephalographic signal that corresponds to mth experiment carried out for one operator
${\mathit{W}}_{mk}=\left[{\tilde{t}}_{m,k},{\tilde{t}}_{m,k+1}\right]$	time area that corresponds to kth zone in mth cycle of electroencephalographic signal
$I_{{\mathit{W}}_{m,1}}\left(t\right)$	indicator function of time area that corresponds to state of operator’s passivity in mth cycle of electroencephalographic signal
$I_{{\mathit{W}}_{m,2}}\left(t\right)$	indicator function of time area that corresponds to state of operator’s activity in mth cycle of electroencephalographic signal