The signs of formal logic and set theory, grouped because they are learned and misread as a set. Four of them come in pairs distinguished only by reflection or by a curve — union against intersection, for-all against there-exists, the sharp logical connectives against their rounded set-theoretic counterparts — and the resemblance is not a coincidence: conjunction on statements and intersection on sets are the same operation seen twice. The group also holds the notation's honest limits, most clearly the subset sign, which no convention has settled on treating as strict or non-strict.
A rounded epsilon meaning membership of a set.
A rounded bracket opening right, stating that one set is contained in another.
A rounded U shape, denoting everything in either of two sets.
An inverted rounded U, denoting what two sets have in common.
A circle crossed by a diagonal stroke, denoting the set with no members.
An inverted capital A, the universal quantifier of formal logic.
A mirrored capital E, the existential quantifier of formal logic.
A pointed caret, denoting conjunction in formal logic.
A pointed V, denoting inclusive disjunction in formal logic.
A horizontal bar with a short downward tick at its right end, denoting logical not.
A double-shafted arrow pointing right, denoting logical implication.
A double-shafted arrow with heads at both ends, denoting logical equivalence.