Editing Subtraction (section)

===Natural numbers===
Subtraction of [[natural numbers]] is not [[Closure (mathematics)|closed]]: the difference is not a natural number unless the minuend is greater than or equal to the subtrahend. For example, 26 cannot be subtracted from 11 to give a natural number. Such a case uses one of two approaches:
# Conclude that 26 cannot be subtracted from 11; subtraction becomes a [[partial function]].
# Give the answer as an [[integer]] representing a [[negative number]], so the result of subtracting 26 from 11 is −15.