# Normalization by Evaluation

- Evaluation = Compute the
*value*of closed expressions (no free variables)- E.g. evaluation of arithmetic expressions in primary school: \((11 + 9) \times (2 + 4) = 120\)

- Normalization = Bring expressions with unknowns into a canonical form
- E.g. simplification in secondary school: \((a + b)(a - b) = a^2 - b^2\)

- Normalization of Evaluation (NBE) = Adaption of an interpreter to simplify expressions containing unknowns