 	if(expr->size==0){
 		return copy_cst_expr(expr);
 	}	
-	if(expr->inf_coeff==NULL || expr->sup_coeff==NULL ){
+	if(expr->inf_coeff==nullptr || expr->sup_coeff==nullptr ){
 		return alloc_expr();
 	}
 	//printf("coming here %zu\n",expr->size);

				else{
					sub->inf_coeff = (double*)malloc((sizeA+sizeB)*sizeof(double));
					sub->sup_coeff = (double*)malloc((sizeA+sizeB)*sizeof(double));
					sub->dim = NULL;
					
					sub->type = SPARSE;
					size_t l = 0;

			//printf("max_l: %gmax_u: %g\n",max_l,max_u);
			//fflush(stdout);
			//expr_t * expr = (expr_t *)malloc(sizeof(expr_t));
			//expr->inf_coeff= expr->sup_coeff = expr->dim = nullptr;
			//expr->size = 0;
			//expr->inf_cst = -max_l;
			
			//out_neurons[out_pos]->maxpool_lexpr = nullptr;//create_sparse_expr(nullptr,max_l,nullptr,0);
			out_neurons[out_pos]->maxpool_lexpr = create_sparse_expr(lcoeff,0,ldim,1);
			//double *ucoeff = (double *)malloc(p01*sizeof(double));
			//size_t *udim = (size_t *)malloc(p01*sizeof(size_t));
