  A superredundant clause is a clause that is redundant in the resolution
closure of a formula. The converse concept of superirredundancy ensures
membership of the clause in all minimal CNF formulae that are equivalent to the
given one. This allows for building formulae where some clauses are fixed when
minimizing size. An example are proofs of complexity hardness of the problems
of minimal formula size. Others are proofs of size when forgetting variables or
revising a formula. Most clauses can be made superirredundant by splitting them
over a new variable.
