Errata to Section 12.8

• Line 1: read "Church-Rosser property in orthogonal systems" instead of "Church-Rosser property".
• Theorem 12.8.2: read "orthogonal iTRS" instead of "iTRS".

Without the restriction of orthogonality the theorem would clearly be wrong. Two different overlapping collapsing rules may give rise to the same collapsing towers, like in the confluent iTRS given by the rules A(x)->x, A(A(x))->x.