The standard German terms for construction contracts, the VOB/B, set out what a contractor must do with a doubt. If he has concerns about the planned method, the materials supplied or another firm’s work, he must tell the client unverzüglich – möglichst schon vor Beginn der Arbeiten – schriftlich: without delay, if possible before work begins, and in writing (§ 4(3)). This document is the Bedenkenanzeige. A contractor whose work is obstructed must also report it in writing without delay (§ 6(1)). If he does not, he can claim the obstruction later only if the client clearly knew about it anyway. The contractor must also prove that he gave notice.