$B_{2} = \# \left\{\left\{\left\{1\right\}, \left\{2\right\}\right\}, \left\{\left\{1, 2\right\}\right\}\right\} = 2$

Definitions:

Fungrim symbol | Notation | Short description |
---|---|---|

BellNumber | $B_{n}$ | Bell number |

Cardinality | $\# S$ | Set cardinality |

Source code for this entry:

Entry(ID("3627de"), Equal(BellNumber(2), Cardinality(Set(Set(Set(1), Set(2)), Set(Set(1, 2)))), 2))