Being an essential and permanent part of something.
Being an included feature that normally comes as an extra.
Constructed as a non-detachable part of a larger structure.
Anything (such as a piece of furniture, or a software feature) that is built in, not added as an extra.
Lasting for an indefinitely long time.
Without end, eternal.
A card whose effects persist beyond the turn on which it is played.
A chemical hair treatment imparting or removing curliness, whose effects typically last for a period of weeks; a perm.
Given an n⨯n matrix a_ij,, the sum over all permutations 𝜋, of ∏ᵢ₌₁ⁿa_i𝜋(i).