Move theorems about hereditarily finite sets to main - #5476
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avekens
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After the definition is moved to main, the theorems about HF sets already in main can (and should) be revised to use this definition, e.g.
ackbij2 $p |- H : U. ( R1 " _om ) -1-1-onto-> _om $=
=>
ackbij2 $p |- H : Hf -1-1-onto-> _om $=
| $( The constant ` Hf ` is a class. $) | ||
| chf $a class Hf $. | ||
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| $( Define the hereditarily finite sets. These are the finite sets whose |
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Something like "(also called HF sets in the following)" should be added to introduce the abbreviation HF.
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Probably the converses of hfuni and hfpw are true. Even though these converses are less useful, the biconditionals would be nice strengthenings in a future PR.
avekens
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This creates a new section about hereditarily finite sets in main by moving much of SF's mathbox section. These include the statements I anticipate using in my mathbox in future PRs.
General rank theorems that are dependencies of HF theorems:
rankpwg
rankung
ranksng
Statements about hereditarily finite sets:
chf
df-hf
elhf
elhf2
elhf2g
0hf
hfun
hfsn
hfadj
hfuni
hfpw