A Zeuthen-Segre invariant is an invariant of complex projective surfaces.

A set function (or setter) is an object mutator. You use it to modify a property of an object such that the object's invariant is maintained. If the object has no invariant, a setter is not required.

A get function (or getter) is an object accessor. You use it to obtain a property from an object such that the object's invariant is maintained. If the object has no invariant, you do not need a getter.

yes

Andrzej Pelc has written:

'Invariant measures and ideals on discrete groups' -- subject(s): Discrete groups, Ideals (Algebra), Invariant measures

If the coefficients of the linear differential equation are dependent on time, then it is time variant otherwise it is time invariant.

E.g: 3 * dx/dt + x = 0 is time invariant

3t * dx/dt + x = 0 is time variant