Natural This type of operate signifies a partial function on naturals, in which the proof of even (n) might be witnessed like a precondition. Within the Cambridge English Corpus There is no serious distinction between the usual first-order objects on the mathematical discourse - including naturals, sets and so on https://share.evernote.com/note/8017dd9b-bae1-b7b2-e7a5-981f51e2ee16