A && B ; C && D を例に考えると、(A && B) ; (C && D) と (A && B ; C) && D はどちらもCが成功したときだけDを実行するわけですから等価です。他の例を考えても完全に等価だと思うのですが、数学的に示せるかはわかっていません。数学的帰納法の出番かなあ…?↩
さいきんRaspberry Pi 4を買ったんですが、Wi-Fiだけで運用したときにRaspberry Piへのアクセスがイマイチ不安定、ということがありました。ネットの情報を調べるとLinuxの無線ネットワークの「パワーマネジメントモード」をオフにすれば平和になるような話が見つかるんですが、その挙動を解説した記事が見つからなかったので自分なりに調べてみました。
$ while true ; do ping -c4 192.168.1.168;sleep15;done
PING 192.168.1.168(192.168.1.168): 56 data bytes
Request timeout for icmp_seq 064 bytes from 192.168.1.168: icmp_seq=0ttl=64time=1793.757 ms
64 bytes from 192.168.1.168: icmp_seq=1ttl=64time=790.571 ms
64 bytes from 192.168.1.168: icmp_seq=2ttl=64time=2.760 ms
64 bytes from 192.168.1.168: icmp_seq=3ttl=64time=6.573 ms
---192.168.1.168 ping statistics ---4 packets transmitted, 4 packets received, 0.0% packet loss
round-trip min/avg/max/stddev =2.760/648.415/1793.757/734.991 ms
PING 192.168.1.168(192.168.1.168): 56 data bytes
64 bytes from 192.168.1.168: icmp_seq=0ttl=64time=703.300 ms
64 bytes from 192.168.1.168: icmp_seq=1ttl=64time=3.618 ms
64 bytes from 192.168.1.168: icmp_seq=2ttl=64time=9.246 ms
64 bytes from 192.168.1.168: icmp_seq=3ttl=64time=9.187 ms
---192.168.1.168 ping statistics ---4 packets transmitted, 4 packets received, 0.0% packet loss
round-trip min/avg/max/stddev =3.618/181.338/703.300/301.364 ms
PING 192.168.1.168(192.168.1.168): 56 data bytes
Request timeout for icmp_seq 064 bytes from 192.168.1.168: icmp_seq=0ttl=64time=1549.241 ms
64 bytes from 192.168.1.168: icmp_seq=1ttl=64time=545.393 ms
64 bytes from 192.168.1.168: icmp_seq=2ttl=64time=2.565 ms
64 bytes from 192.168.1.168: icmp_seq=3ttl=64time=9.234 ms
---192.168.1.168 ping statistics ---4 packets transmitted, 4 packets received, 0.0% packet loss
round-trip min/avg/max/stddev =2.565/526.608/1549.241/630.164 ms
PING 192.168.1.168(192.168.1.168): 56 data bytes
64 bytes from 192.168.1.168: icmp_seq=0ttl=64time=455.575 ms
64 bytes from 192.168.1.168: icmp_seq=1ttl=64time=3.466 ms
64 bytes from 192.168.1.168: icmp_seq=2ttl=64time=9.315 ms
64 bytes from 192.168.1.168: icmp_seq=3ttl=64time=3.040 ms