  Relativistic methods for the Foldy-Wouthuysen transformation of the
``step-by-step'' type already at the first step give an expression for the
Hamilton operator not coinciding with the exact result determined by the
Eriksen method. The methods agree for the zeroth and first orders in the Planck
constant terms but do not agree for the second and higher-order terms. We
analyze the benefits and drawbacks of various methods and establish their
applicability boundaries.
