Defaulting export of all defined names if (export) form is absent

[alvatar]

Library:

(define-library (spheres/math/exact)
    (export double) ; <-- If commented, 
    (import (gambit))
    (begin
      (define double (λ (x) (* 2 x)))))

Code using the library:

(define-library (asdf) (import (gambit) (spheres/math/exact)) (begin (pp 'asdf)))

If (export) isn't used, then:

*** ERROR IN (console)@10.71 -- Unbound variable: spheres/math/exact#pp

Should the (export) clause be mandatory? If so, a warning/error should be emitted when absent.