Normal form (natural deduction)
In mathematical logic and proof theory, a derivation in normal form in the context of natural deduction refers to a proof which contains no detours — steps in which a formula is first introduced and then immediately eliminated.
The concept of normalization in natural deduction was introduced by Dag Prawitz in the 1960s as part of a general effort to analyze the structure of proofs and eliminate unnecessary reasoning steps. The associated normalization theorem establishes that every derivation in natural deduction can be transformed into normal form.