The authors describe systematic methods for uncovering scientific laws a priori on the basis
of intuition or Gedanken Experiments. Mathematical expressions of scientific laws are by
convention constrained by the rule that their form must be invariant with changes of the units
of their variables. This constraint makes it possible to narrow down the possible forms of the
laws. It is closely related to but different from dimensional analysis. It is a mathematical
book largely based on solving functional equations. In fact one chapter is an introduction to
the theory of functional equations.
