A variable definition binds one or more identifiers and specifies an initial value for each of them. The simplest kind of variable definition takes one of the following forms:
(define ⟨variable⟩ ⟨expression⟩)
(define (⟨variable⟩
⟨formals⟩) ⟨body⟩)lambda expression). This form is
equivalent to
(define ⟨variable⟩ (lambda (⟨formals⟩) ⟨body⟩)).
(define (⟨variable⟩ . ⟨formal⟩) ⟨body⟩)(define ⟨variable⟩ (lambda ⟨formal⟩ ⟨body⟩)).