Originally, resources are the environment of the problem. They are also part of the problem.
As told in the third postulate, "a good solution is a solution is a solution that involves as few new resources as possible".
So we have to check with the existing resources which of them can help us.
There are four types of resources. Each of them can be simple or combined.
These resources can be in different states:
solid
liquid
gas
plasma
mechanical
thermal
chemical
electric
magnetic
One trick to memorize: MATHEM, for Mechanical, Acoustic Thermal Electric Magnetic
before action
during action
after action
Void
gap
spacing
place