8. All productivity is based on three factors: 1) natural resources (NR), whose form, place and condition are changed by the expenditure of 2) human energy (HE) (both muscular and mental), with the aid of 3) tools (T).

This is straight forward enough. These three factors make up the totality of the economy. As a formula, this is seen as NR + HE x T = Man's Material Welfare.
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