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Theorem del-size

⊦ a ∈ s → #(s -- a) = # s - 1

Type: A user defined theorem
Validity: The proof is valid.
Features: s, ls, localcut,
Comment:
Used by: del-size-01, del-size-02, del-three, diff-sub-size, size-del-leq, union-size-02,
Used by units in proved state: oset, ostore,
Proof exists?: Yes

View the proof

Infos about the proof

Proved?: Yes
Interactions: 1
Proof steps: 3
Used lemmas: del-in, del-addeq-05,
Used spec theorems:
- set-basic/indef
Used simplifier rules: