  This paper introduces a symbolic calculus to evaluate the output signals at
the target line(s) of quantum computing subcircuits using controlled negations
and controlled-Q gates, where Q represents the k-th root of [0 1; 1 0], the
unitary matrix of NOT, and k is a power of two. The controlling signals are
GF(2) expressions possibly including Boolean expressions. The method does not
require operating with complex-valued matrices. The method may be used to
verify the functionality and to check for possible minimization of a given
quantum computing circuit using target lines. The method does not apply for a
whole circuit if there are interactions among target lines. In this case the
method applies for the independent subcircuits.
