Let G be a finite permutation group on Ω. An ordered sequence of elements of Ω, $({\omega }_1,\dots ,{\omega }_t)$, is an irredundant base for G if the pointwise stabilizer $G_{({\omega }_1,\dots ,{\omega }_t)}$ is trivial and no point is fixed by the stabilizer of its predecessors. If all irredundant bases of G have the same size we say that G is an IBIS group. In this paper we show that if a primitive permutation group is IBIS, then it must be almost simple, of affine-type, or of diagonal type. Moreover we prove that a diagonal-type primitive permutation groups is IBIS if and only if it is isomorphic to $\mathrm{PSL}(2,2^f)\times \mathrm{PSL}(2,2^f)$ for some $f\ge 2$, in its diagonal action of degree $2^f(2^{2f}-1)$.

令G为 Ω 上的有限置换群。Ω 的有序元素序列，$({\omega }_1,\dots ,{\omega }_{吨})$, 是G的冗余基，如果点稳定器$G_{({\omega }_1,\dots ,{\omega }_{吨})}$是微不足道的，它的前辈的稳定器没有固定任何点。如果G 的所有冗余基都具有相同的大小，我们就说G是一个 IBIS 群。在本文中，我们表明，如果一个原始置换群是 IBIS，那么它必须几乎是简单的、仿射型或对角线型的。此外，我们证明对角线型原始置换群是 IBIS 当且仅当它同构于$\mathrm{PSL}(2,2^F)\times \mathrm{PSL}(2,2^F)$ 对于一些 $F\ge 2$，在其度的对角作用 $2^F(2^{2F}-1)$.