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Theorem
A statement from that can be proved without any given premises
Justified step
Either a premise, or an assumption, or a step that follows from previous step according to one of the given rules of inference
Proof
Sequence of justified steps in which last step is desired conclusion; that is, it is a sequence of steps, each of which is either a premise, or an assumption, or a step that follows from previous steps according to one of the given rules of inference and in which the last step is the desired conclusion
Statement variable
Letter that can take as a substitution instance any particular statement, simple or complex
Statement constant
Capital letter that is used as an abbreviation for a particular truth functionally simple English sentence
Statement
Formular that has statement constants as its smallest components
Statement form
Formula that has statement variables as its smallest components
Substitution instance
Statement form is a statement obtained by substituting some statement for each variable in the statement form
Derivation
Sequence of justified steps
Proof
Derivation in which last step is desired conclusion