mk_absTerm.mk_abs : term * term -> term
Constructs an abstraction.
mk_abs (v, t) returns the lambda abstraction
\v. t. All free occurrences of v in
t thereby become bound.
Fails if v is not a variable.
Term.dest_abs, Term.is_abs, boolSyntax.list_mk_abs,
Term.mk_var, Term.mk_const, Term.mk_comb