@SK53 @grischard I was curious so I wrote a small Python script, here are the most frequent pairs in the #OpenStreetMap database! ☺️

1) "guest_house=guest_house" : 4218
2) "entrance=entrance" : 2213
3) "government=government" : 2206
4) "memorial=memorial" : 2048
5) "fitness_station=fitness_station" : 1802
6) "swimming_pool=swimming_pool" : 1078
7) "marker=marker" : 753
8) "wall=wall" : 642
9) "construction=construction" : 585
10) "substation=substation" : 523