 Church-Rosser property of a reduction relation

A reduction relation has the Church-Rosser property when its equivalence relation generated by forward and backward steps satisfies $b{\leftrightarrow }^{\ast }c\Rightarrow \exists d(b{\to }^{\ast }d{\leftarrow }^{\ast }c)$. It is equivalent to confluence of ${\to }^{\ast }$. The Church-Rosser theorem establishes it for beta reduction.