R’ Eliezer says: If one did not bring an instrument [for circumcision] before the Sabbath, he should bring it on the Sabbath exposed; and in [times of] danger, he should cover it in the presence of witnesses. Furthermore, said R’ Eliezer: We may fell trees in order to make charcoal and to form an iron instrument. [But] R’ Akiva stated a rule: Any work that can be done before the Sabbath does not override the Sabbath; but [any work] that cannot be done before the Sab-bath does override the Sabbath.