Process for preparing at least one partial oxidation andor ammoxidation product of propylene, in which the propylene is produced from crude propane by dehydrogenation and is subjected to a heterogeneously catalyzed gas-phase partial oxidation andor partial gas-phase ammoxidation in the presence of unreacted propane as constituent of a gas mixture 2 containing <1% by volume of 1-butene. The access authorization is verified by analysis of a voice signal which was entered by the subscriber placing the call, before or during a call in progress. An interleaver applies a predetermined interleaving pattern to the encoded message. The OPO generates up to 27 OmW of average power across the available tuning range and can deliver femtosecond pulses at a repetition rate of 76 MHz. Nozzle mounting assemblies may be adapted to a variety of pool types and surfaces, and may be sized for the floor surface, the steps or the walls of a swimming pool. The break down of the rock fabric at the tunnel tip, caused by the near-instantaneous overpressure generated within the tunnel, further creates substantially debris-free tunnels in conditions of limited or no underbalance as well as in conditions of overbalance.