Express the user's need in terms of function = level 0
Functional analysis: expressing needs in terms of functions and methods for finding functions

The user's needs are often set out in specifications. Using the user's specifications as a starting point, supplemented by your investigation, transform the need into simple expressions.

Find a simple expression for the product's fundamental need. This is the expression of the Level 0 need. Use a verb and a complement.

Without this primordial function, known as the main function (FP), the product would not exist.

In our examples for the "redesign" or "creation" of a product, the hypotheses constitute the user's specifications (see "Redesigning" a product with functional analysis: preliminary work and the steps involved