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bvar                                                            (Term)
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bvar : term -> term

SYNOPSIS
Returns the bound variable of an abstraction.

DESCRIBE
If {M} is a lambda abstraction, i.e, has the form {\v. t}, then
{bvar M} returns {v}.

FAILURE
Fails unless {M} is an abstraction.

SEEALSO
Term.body, Term.dest_abs.

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