while

A is contained in B, and B is contained in A, that is to say, A=B is added to the true inclusion.

When a and b are not equal, true inclusion can be used.

Use a true inclusion that does not contain equality, and use an inclusion that contains equality.

Tolerance is not equal to equality. Inclusion only means that there is the possibility of "equality" in it, and there may be other situations that are not included. Equality is just a situation.