Given a coupling function \(c\) and a non empty subset of ℝ, we define a closure operator. We are interested in extended real-valued functions  whose  sub-level sets are closed for this operator.  Since  this class of functions is closed under pointwise suprema, we introduce a regularization for  extended real-valued functions. By decomposition of the  closure operator using polarity scheme, we recover the  regularization by bi-conjugation. We apply our results to derive a strong duality for a minimization problem.