# In a polyhedron with vertices, if a vertex has two basic feasible basis, is there a redundant inequality?

We consider a polyhedron $P = \{ x \in \Bbb R^n \mid Ax \leq b\} \neq \emptyset$, $A \in \Bbb R^{m \times n}$, $b \in \Bbb R^m$, $A$ with full column rank. With those hypotheses, we know that $P$ has vertices.

Each vertex $v \in P$ can be described by a set of rows of $A$ indexed by $B \subseteq \{1, ..., m\}$, called a basic feasible basis, such that $\lvert B \rvert = n$, the submatrix $A_B$ (the rows from $A$ indexed by $B$) has full rank, and $A_Bv = b_B$.

We have degeneracy when a vertex can be described by two different basis. If this happens, does it mean that $P$ has at least one redundant inequality (i.e. one that can be deduced from the others) ? If not, what hypotheses should we add to avoid degeneracy ?