  The purpose of this paper is to collect the homotopical methods used in the
development of the theory of flows initialized by author's paper ``A model
category for the homotopy theory of concurrency''. It is presented
generalizations of the classical Whitehead theorem inverting weak homotopy
equivalences between CW-complexes using weak factorization systems. It is also
presented methods of calculation of homotopy limits and homotopy colimits using
Quillen adjunctions and Reedy categories.
