A Corollary
No, a corollary follows from a theorem that has been proven. Of course, a theorem can be proven using a corollary to a previous theorem.
Oh yes, the Pythagorean Theorem has been proven.
That is a theorem.A theorem.
A corollary.
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a theorem
No it would be a theorem if it was proven.
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Axioms within the system, definitions, theorems "already proven" (not relying upon this theorem directly or indirectly for truth), and logic.
Neither. A theorem is a proven mathematical statement. This says nothing about how easily it can be proven. e.g. the Pythagorean Theorem is easily proven, but Fermat's Last Theorem is extremely difficult to prove.
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theorem