Online Algebra Calculator
Many of users do not use powerful Maxima computer algebra system for systematic work, but for ad hoc algebraic calculations – equations, functions, matrixes, etc. only. To do this job, it is not useful to download the whole application from a web site.
Function: disjoin (<x>, <a>) Returns the set <a> without the member <x>. If <x> is not a member of <a>, return <a> unchanged.

disjoin complains if <a> is not a literal set.
disjoin(<x>, <a>), delete(<x>, <a>), and setdifference(<a>, set(<x>)) are all equivalent. Of these, disjoin is generally faster than the others.
Examples:
(%i1) disjoin (a, {a, b, c, d});
(%o1) {b, c, d}
(%i2) disjoin (a + b, {5, z, a + b, %pi});
(%o2) {5, %pi, z}
(%i3) disjoin (a - b, {5, z, a + b, %pi});
(%o3) {5, %pi, b + a, z} There are also some inexact matches for disjoin. Try ?? disjoin to see them.
(%o1) true (%i2)