Carillon strike the inside of the bells, allowing the performer on the bells, or "carillonneur/carillonist" to vary the intensity of the note according to the force applied to the key. Although unusual, real carillons have occasionally been fitted to theatre organs (instead of the metal bars or chimes more often used in simulation), such as the Christie organ installed at the Regal Cinema, Marble Arch, in London. A carillon-like instrument with fewer than 23 bells is called a chime. The carillon is the second heaviest of all extant musical instruments, only ranking behind the largest pipe organs. The heaviest carillon in
Partition of a set "coarser" than "α"—if every element of "α" is a subset of some element of "ρ". Informally, this means that "α" is a further fragmentation of "ρ". In that case, it is written that "α" ≤ "ρ". This "finer-than" relation on the set of partitions of "X" is a partial order (so the notation "≤" is appropriate). Each set of elements has a least upper bound and a greatest lower bound, so that it forms a lattice, and more specifically (for partitions of a finite set) it is a geometric lattice. The "partition lattice" of a 4-element set has 15 elements